It's not really a question of whether communities have a "right" so much as that I don't think it's something that Reddit should support, but they provide moderator tools to do this. Worse yet, they bring this problem upon themselves by making it ridiculously easy to setup dummy Reddit accounts and can be active in a very short period of time, which practically encourages ban evasion. Instead of allowing innocent users to face guilt by association, Reddit should add a lot more friction to creating new accounts and add read-only period.

> My buddies and I have no obligation to let you hang out with us if we don't like your politics.

There's nothing wrong with this in principal, except the default behavior for subreddits is to allow literally anyone to "join" in a single click. Those people aren't all your "buddies". A community can become private, but this also means not being visible to anyone except members. This creates a weird dichotomy where either a community is full-blown open and is encouraged to use other people's subscriptions against them, or to be invite only but few want to join because they can't see the activity of the site.

> I certainly don't care for the way Reddit runs its "communities". They are, in practice, run by a variety of petty tyrants.

That's exactly why the guilt-by-association approach frequently goes overboard.

> The solution to that is not, in my opinion, to increase centralized control even more.

Agreed. Some better approaches would be to allow a middle-ground for communities to be more exclusive and for sock puppet accounts to no longer be piss easy to create.