Maybe these social networks could be manage by the community. A bit like HN. Here if you post crap, people can downvote your crap to the bottom so that no one can see it.

If you want to be seen and red, you need to post quality and gain reputation. People with bad reputation will slowly lose visibility.

It might not work, but clearly it seems that quality is a prime factor on HN and it's one of the reason why I trust more HN than any other social network.