No one's going to change a tiny picture that does no harm just because a few people don't like it.
God damn I barely even pay any attention to them when I browse the forums.
It goes deeper than the actual avatar itself.
Brony pride is the biggest problem.
Think of it this way, if you walked into your favorite bar, and then you see a group of people there are naked there trying to show off their richards, and they're intending to come there again for the next few years, you're disgusted and you complain, but they say "No! if you don't like us doing this, don't come here again!"
And the manager of the bar says nothing on it, so he can't help.