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True, but the idea that we voluntarily participate makes the concept more community based and less policed. I'm guessing an upvote and downvote, like on YouTube, will eventually replace flagging with the same effect.

Sure.

an upvote and downvote, like on YouTube, will eventually replace flagging

Afaik, initially it was launched exactly like that, but after some time downvote was replaced with flag under pretext that people "downvote to much" and that should be somehow discouraged.