The stigmatization of the autodidact may not be unique to the field of composition, but the field of composition certainly has a unique way of stigmatizing autodidacts. I've often been the first one to come to their defense, if for no other reason than that I (marginally) count myself as one. Nonetheless, I often ask myself if there is really any such thing as a self-taught composer in the first place. I've learned so much about structure, harmony, and orchestration just by playing music (to say nothing of listening) that I sometimes don't feel the autodidact label is even appropriate, either in the sense that it implies general unstudiedness, or in the sense that anyone comes about these things purely through self-discovery. My discomfort with the label is only intensified by the experience of working with "real" autodidacts, who identify me immediately and intensely as an academic product, which I am in most every other way.
As a younger person, I held in high regard the elusive (and ultimately implausible) idea of "pure" creativity, free from any influence of any kind, and rebelled intently against the idea of embracing overt musical influences. As time has gone on, I've had an easier time accepting the idea of synthesis, in part simply by having heard more music*. Not only does this greater depth of experience make it easier to hear the myriad threads of influence in particular areas of music much more clearly than before, but it also leads naturally to the realization that the more varied the sources, the less overtly the synthesized product betrays any one of them to the listener (I say "naturally" because the difference is obvious when I look back at my very earliest efforts and compare them to more recent ones; hearing them now in all their derivative splendor, it's no wonder I was so insecure about influences). Conversely, so-called "pure" creativity is implausible because it requires that one not be aware of any other music at all, and as such, unaware that the phenomenon of music exists in the first place. Anyone who gets around to writing music at all has undeniably learned something beforehand, but whether they taught it to themselves per se is debatable.
You may not be any more original than you were before, but a greater number of sources at least makes you sound that way. It's a bit of a paradox, but learning to live with it is a crucially important part of composition. I certainly didn't reach this conclusion in a lesson, but I wouldn't go as far as to say that I taught it to myself either.
*As an aside, I feel it's worth mentioning also what a powerful negative influence it has been to come across self-promoting nutcase after self-promoting nutcase claiming to be doing something original when all too often they end up sounding not just a little bit derivative, but extremely so. Once it became impossible to imagine myself getting far enough away from my influences to feel comfortable acting that way myself, I decided that there was no reason to anyway. (To qualify that last statement just slightly, I still very much believe in the values of "creative" music, whatever that is, over authenticity fetishism and revivalism. I think that there's a strong case to be made in its favor, and definitely have some unfavorable things to say about the most particularly non-creative people out there, even if they're not avid self-promoters, but that will have to wait for another time.)