[derefr]

The only eventual result of "people upvoting things relevant to them" in an open-membership community is the upvoting of the things the most people can agree on: pictures of cats with words on them. Communities on the internet have disparate purposes, and must be tended--if not by editors, then by the conscientious decisions of their members--lest they all become pointless microcosm-representations of society as a whole. And yes, this sometimes involves being "that guy" and telling people to think more about the net effect of everyone voting the same way they do (in a Timeless Decision Theory sort of way) before they upvote things.

[cantos]

There are two things wrong with this. First, you are assuming that a nonzero fraction of people will sign up for every open-membership community available to them, frequent, and vote in each such community. Realistically most people probably can't do this for more than ten communities. Second, even if there is eventually convergence it may not occur quickly. For example, the universe will eventually reach a state of maximum entropy but it isn't something that any of us need to worry about today.

[notdrunkatall]

If that happens here, we'll find another place, ad infinitum. That's just how it works.