At the end of the day, you have to filter on quality.
All you end up doing is implementing another ham-fisted DRM scheme that ultimately accomplishes nothing but makes the pointy-haired bosses happy. Solving social problems like this with "moar technology" is, in the general case, not a recipe for success, and I don't see why this would be any different.
LinkedIn is actually better off than most sites, because it already has a "people you actually know" filter built in. If you've connect to randoms, you'll get random content. But if you connect only to people you know, you have a decent filter. And if people you know start posting rubbish, block them.
Any pseudoymous sites are in a worse position, because you can't tell a person from a bot.