The problem with the idea that Reddit should keep these communities around to prevent something worse happening is that it's depending on the idea of Reddit as thousands of small platforms instead of one large one with a lot of smaller groups. You can see the results of this attitude when you go on YouTube and you see a significant amount of MRAs and alt-righters in your recommendations despite you never wanting to hear a word they say. Why is that? It's because they're being permitted to stay on a platform that pushes their content. If alt-righters were banned from YouTube on a regular and consistent basis, it's absolutely correct that they would probably just make a video site of their own, but then people would have to seek out that website, or seek out that app for their tablets and phones, and suddenly we're not running into the problem where your six-year-old comes downstairs crying about how feminism is cancer because YouTube's algorithms decided that the perfect companion to his Minecraft videos would be Milo Yiannopoulos and Sargon of Akkad.
While they have good intentions, the people who come into discussions like this saying "well [website] is good because of this subcommunity, I just avoid that subcommunity" are feeding the problem. The more popular Reddit grows for its non-hateful communities, the more attractive a platform it is for its hateful ones. Not only does it normalize these hateful communities, it also gives them easy access to other areas of the site, and suddenly you have incidents like, anecdotally, an influx of Steven Crowder fans who were able to successfully recruit members of r/Radiohead despite them being the most lefty left leftist band this side of Pussy Riot.
It's easy for people to write off and forget about hateful communities when they're confined and are specifically dedicated to hatred - Stromfront and other white supremacist websites existed long before the alt-right did, but nobody gave a shit about them because they knew only awful people went to those websites. If you sign up for Stormfront, you are automatically an awful person. If you sign up for Reddit, you aren't, and it's specifically that ambiguity that hate groups look to exploit.
