The problem with questions like this is that, if you actually did get people sharing quality responses of where to go (and there are good alternatives), there's

The problem with questions like this is that, if you actually did get people sharing quality responses of where to go (and there are good alternatives), there's no way to filter who sees those links. In other words, the people who you consider "undesirable" will most certainly see those links, follow them, and some will create accounts at those new places thus bringing the same "problem" to the new site. Are there boards/communities that do what you want? Absolutely! But the members who are cognizant of how "special" that community is will protect it. A lot of people learned how to do this after what happened to the various sites that became popular (like HN). Were things different five years ago? Damn straight. But it happens - sites become popular, people move on, and the cycle either starts over or people lose interest.