Summary: I would like to question why house-elves have turned out the way they have; what is it in their history that has made them emerge, seemingly, as the perfect servants for the human race?
Where exactly did the house-elves come from? It's an easy enough argument to say that S.P.E.W. is ill-conceived, or that elvish rights are a waste of time, because house elves seemingly like being servile to humans, but every species has its own complex and rich history, and the origin of the house-elves is never considered or even mentioned. The most dominant and interesting aspect of house-elves' traits is the servility they show to humans. I would personally question whether it is simply because 'they like being enslaved' (Goblet of Fire, page 211), and wonder why that would be. Is it, for example, because they are genetically predisposed to be servile and to enjoy enslavement, as an inherent part of their genetic make-up as a species; or is it because they have been selectively bred by humans (bearing in mind that humans are generally larger and stronger than house-elves) to become this?
Let us consider the first argument: that elves are simply, genetically, slaves. At first glance, it seems unlikely; in a wild, hostile environment in which house-elves would have evolved (considering that we are given reason to believe that they are natural species which have developed just like goblins or humans, rather than something created artificially by humans, for humans), they would have died if their first instinct was to throw themselves at the feet of anything larger and stronger which came their way. I find it difficult to believe that, in a world where it truly would have been 'survival of the fittest', such a meek and eager-to-please disposition would have been favoured. However, it is possible that house-elves would have chosen to hide rather than seeking conflict; but this does not explain their seemingly inbuilt need to please and be obedient to a separate species, even when it treats them so appallingly.
Then consider that they could have gravitated towards humans for protection as human society evolved and the elves saw them as a greater power who would protect them. The 'slave' status may have emerged later, when humans saw that they could take advantage of this species who slid so well into the role of the obedient working class. When elves first started to be employed in the service of humans, presumably, the elves who had this larger, more powerful species protecting them - and were therefore less proud, less confident, and more likely to have traits that we see in contemporary representations of house-elves - these would have been the elves who bred most, no longer fearing natural predators, and passed on their personalities to their young. Remember, too, that they would also have taught their children to be obedient to their masters, so as to secure them futures with jobs and safety for life. If the enslavement of the elves came in staggered stages, it is easy to imagine that the society of the contemporary elves would have bifurcated: the safe, cosseted, mild-mannered type that we see today; and the wilder, prouder members (maybe reminiscent of the elves, or even hobbits, in Tolkien's work) who would refuse to bow to the will of another species, but would perhaps later fall prey to a greater enemy. Vicious predators or an epidemic of some plague or Spanish flu-esque disease could easily wipe out these remaining elves, therefore leaving us only with the tame kind we see today. However, nowhere is it ever denied that house-elves might exist in the wild; some may still be out in the forests or mountains, or perhaps on the plains or underground. Is there any evidence to indicate that the house-elves we see enslaved by humans are the only type, or are there others, having broken off from their humbler cousins, still somewhere in the Potter universe?
The second argument indicates a rather more sinister affair. It is possible that humans, finding these timid, easily-subdued, humanoid creatures in the wild, could have gone about manufacturing themselves slaves, whose very personalities - and, later, society - would cause them to recoil even at the idea of freedom. Therefore, the evolution of the elves would not be a natural, elf-governed affair, but a deliberate and systematic approach to creating human supremacy above these smaller counterparts. Consider, again, the elves coming into contact with the humans and, whether because the elves chose to do so or because the humans wheedled them into doing it (with words or imprisonment, it will never be entirely clear), deciding to enter their service. The humans would then have control over the elves, enough to decide which should breed, and continue their compliant traits, and which should not. It takes no imagination at all to imagine that humans would kill or suppress elves who did not bend so easily to their will, considering the way we see elves treated in the 1990s during the series, or the way humans have treated one another in the past. Elves did not suddenly spring up in stately homes; they, at some point, entered human service, and I imagine there must be some elves who did not simply bend to the will of their human 'masters'. I personally would love to see if, behind this veneer of timid servants stretching back into history, there was a bloody and violent past. What happened to the free elves? Did they all enter service, without so much as a whimper; did they all die of natural causes, or were they hunted down by humans; or do they still exist somewhere, with temperaments as fiery as those of goblins? Is it even possible that goblins and elves shared a common ancestor and, like the Morlocks and Eloi, developed into two totally separate species, with humans holding an unusual balance between the two?
One could argue, of course, that the lack of history of elvish rebellions (for surely Hermione would have found some, were there any to be uncovered) indicates a lack of potential historic warfare. I would like to propose an alternative explanation: that humans, presumably the species most specialised in written histories and the written word, either never noted down any indications of elvish non-compliance, or destroyed any records later on. Think of the book-burnings in Nazi Germany, when by destroying the written word they tried to remove the very culture of the people they wished to subdue. Fortunately, we have copies of most of the books they tried to eradicate because they were preserved by individuals, either secretly in Germany or in other countries; but it is likely that elves would have no such opportunity. How would elvish society go about preserving their knowledge, or knowledge which referred to them? Firstly, do we even know if they can read and write (and if so, whether they could read and write the language of their masters)? Who would stand up for the elves in a situation where humans were systematically destroying evidence of their less subordinate history? Not humans, surely; not with regards to a species that, by this point, would surely be seen exactly as we know them to be in the 20th century. And not elves. The ones who had been in the service of humans for years would surely not dare to defy their masters, if any such grain of resistance existed in their characters anyway; and if they did, where would these histories go? With no contact with the outside world, depending wholly on their human families for homes and protection, they could not hide it in their own lives. If wild elves still existed, I imagine they would have nothing to do with their subservient cousins - and if they did, there is no way any material they took on behalf of the 'civilised' elves would make its way back into human history. The best we can hope for is buried manuscripts, unlikely ever to be found in situations beyond chance. This is all assuming that a removal of elvish history was made public; it would probably have been easier, and less likely to incite resistance, to do all of this in the shadows, without the public ever knowing what they were doing. Besides, if such a destruction were made well-known, there would surely be records of it in human history books - and as far as we know, no such record exists.
Any removal of written work pertaining to elves could also have been a part of something greater which I believe must exist. What do we see of elves, of their lives and culture, outside of what humans attribute to them? Whilst we must acknowledge that the Harry Potter series is an imperfect source, where we only see elves from human eyes and in relation to the humans involved, I think we must conclude nevertheless that very little exists. What a strange thing, for a self-aware and seemingly intelligent (certainly intelligent enough to pick up language and customs without any apparent difficulty) species to have such a lack of identity. I must conclude that it is likely that humans would, in the past, have deliberately gone about removing an 'elvish' sense of identity. We see no evidence that elves have their own language, for example, despite the fact that they can clearly pick language up (which would indicate both a mental capacity to do so and the mechanics - vocal chords, et cetera - needed). Their curious idiosyncracies in English speech - always referring to themselves in third person, for example - makes me wonder whether they do indeed have their own language, forbidden to be mentioned in 'polite (i.e., human) society', in which they have no identity of self but only of others, hence their difficulty in using first-person. Or, when teaching elves how to speak, they may be forbidden to speak of themselves in first-person, since that use would indicate that they have a sense of self, of individuality, of identity that does not relate to their masters. They refer to themselves as their masters refer to them, not as their own people. Is this symptomatic of an identity and society crushed by their overbearing masters, who want not companions or intelligent equals, but slaves who will bend unquestioningly to their will? We see no examples of elvish art, either, either written or visual; we hear no myths or stories that they have made themselves; we only see elves as mini-humans, servants to the family or establishment they serve. I would love to see what happened in their history to make this so. Or is it possible that it still exists, hidden to outside observers and hiding behind their coy facades?
The complete absence of elvish identity and history other than what humans give them seems to me curious and suspicious. I don't believe that elves were 'destined' to serve humans, because they are a species apart and should be considered thusly. Whether this is because they are 'uneducated and brainwashed' (Goblet of Fire, page 211) or because it is genetic is certainly up for debate, but I simply cannot believe that a ready-made 'servant species' just popped up out of nowhere to serve the likes of the Malfoys.
He therefore had to endure over an hour of Professor Trelawney, who spent half the lesson telling everyone that the position of Mars with relation to Saturn at that moment meant that people born in July were in great danger of sudden, violent deaths.
Goblet of Fire, Chapter 20, Page 345
A picture of Gandalf the Grey (from The Lord of the Rings) can be seen in the collection of great wizards in Professor Dumbledore's study in Harry Potter and the Chamber of Secrets.