Why does the alt-right have issues with them being banned from systems, but don't see issues with themselves banning others from systems. For example, Twitter bans them from using Twitter, but the /r/The_Donald echo chamber bans anyone with a counter view to their own. If you want freedom to speak on certain platforms, you need to provide the same rights to everyone.
If they started banning your Reddit account for being a communist, I imagine a lot of people - including "The Donald" - would be angry.