The important part: the group was not banned for their beliefs or their speech. It was banned for violating the TOS, in particular for doxxing.
That site has turned into an utter hole in the last 10 months, regardless of the fact that it was on a steady decline already. I'm not sure if it can be brought back to center where it used to be or if it's better to "nuke it from orbit."
For example the famous Milo Twitter case where Milo himself got banned, but all the radical black hate groups and the actor herself who was posting tons of racist content didn't even get warning but instead tons on sympathy.
I'm not a fan of alt-right, but for news and social media websites, being so disgustingly biased and trying to help the radical leftist agenda is one of the major reasons why things like Trump and Brexit happen.
Their subreddit is purely just linking to comments they disagree with and find the most "disgusting". They can put as many disclaimers as they want but I just don't see how a subreddit that is purely there to link to comments they absolutely hate, can lead to anything but harassment.
You can always start one that isnt called "altright" but you're less likely to get eyes on it which may be the entire point.
They're well within their rights to ban whomever they want, but they should be upfront about deleting subreddits that dont align with them politically rather than this game they're playing finding some TOS reason to remove an entire topic from the site. It doesn't make sense otherwise to punish everyone for the actions of a few.