Why can't we filter out users / topics that we don't like?

The reason for this is that a subreddit is supposed to be a community that agrees on what kind of content they want and don't want to see. The upshot of this is that those that vote are essentially setting the tone of a subreddit for the (huge number of) people who don't ever log in. If those logged in people filter out stuff they don't like, rather than downvoting it, they'll end up leaving that trash for the unlogged people to see. Not very nice! source
and
The fewer people we have voting down the crap, and more crap we get. Since our user-base is always growing, the makeup of the community is changing all of the time, generally based on the content that's currently popular. If the front page is all "Does anyone else like boobies?" then the only new users coming in will be the ones looking to talk about how much they like boobies. Eventually the content you like will dry up because the people that didn't come for boobies and "does anyone else" will leave.
You're actually making reddit better by downvoting the crap you don't like source

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