The only time that I can actually see this happening is in the very late future (assuming MLP continues to exist and attract Bronies) or right now. I say this, not because of the oddity of our interests, but rather the tolerance of that interest. Today, the world is rampant with religious intolerance. There a few reasonable persons, but the ones who are getting the most attention are (obviously) the ones who say 'X Religion should be abolished!' or 'Creationism should be taught in schools!'. However, these movements and thoughts are certainly toning down[1].
How does this tie in to Bronies? Tolerance, or, to be more specific, intolerance. The minds of today usually judge things at first glance and firmly remain in that opinion unless the evidence that goes against that opinion is forced upon them. Even then, they may choose to ignore it. The only chance (besides, as stated previously, the late future) of a large movement to end 'Bronyism', if you will, happening is if it happened within the next year or so. Why? Because of the mindset most commonly adopted by people today. Yet, we haven't seen anything to shut this down. Why is that? For the same reason the mindset is here in the first place. People's intolerance of things are more focused on things such as religion, LGBT, atheism, etc. rather than these groups that like a T.V. show for girls. Weird? From their perspective, yes. Weird enough to start riots in the streets? Most certainly not. To do so would simply draw more criticism from others than the Brony 'movement' itself because the issue is so insignificant on the grand scale.
I say it could happen in the future for the same reason it could happen today. The mindset of intolerance will return, except it will probably be about different things. But, in the end, the chances of it's happening is so small that it's not even worth thinking about.
There's my input on the matter.
-IP
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[1]http://www.freedomrequireswings.com/2013/06/exodus-international-shuts-down-leader.html