It's just like anything else. The bigger or more popular something gets, the more it is forced to appeal to the lowest common denominator. Shouldn't really be a surprise. I don't think it matters what it starts out as. Just like everything else, it evolves. You might not like it, that's your prerogative. You can choose to spend your time and energy fighting to preserve or change it. Or go elsewhere and/or build something new that's more to your liking.
I think it's interesting that we all seem to feel some sort of 'ownership' of 'internet' things. Ultimately though, most of these 'things' are corporately owned. So, although I do appreciate free speech, does a privately owned online forum have any obligation to ensure and enforce complete and total free speech? Should it really have no control over what it is used for? Or what is said or displayed on it? On one hand I would say hey, whomever exactly it is that actually OWNS Reddit, is free to do what they please with it. Including censoring it or completely shutting it down if they wanted. They are, in fact, a business trying to make money. So, in that respect, the simplest and easiest thing to do (just like with anything else) is, if you don't like it - don't provide them with a source of income with your presence and participation or purchase.
Everyone is entitled to free speech, but you're not exactly free to walk into my living room and start shouting what you want right? I have the option call the police and have you removed, the option to walk away from you, or not read the flyer you posted, etc. Reddit isn't a publicly owned forum - so in the end I think it is their choice. And like I said earlier, they are a business and will work to please the majority at the sake of the minority. And that's, just business right?