While I do and don't agree with @Shedletsky (dev resources are limited and should be put to high value features, this is a somewhat solved problem with MOSS and others...and yes, it will never catch a determined bad actor), I think @Mirroar makes a good case that those who offer code should get some benefit, otherwise they may not be so altruistic.
And @Syncaidius, sure, the fun is in solving problems, but for me, I learn a lot more from seeing how other people have implemented and building onto that...I'd be completely lost and probably would have abandoned a long time ago if I couldn't use someone else's framework as a starting point.
Either way, I think there may be a "Gamification" solution to code sharing that lets people who write unique code measure themselves accordingly, whilst also allowing of us who aren't great devs, learn from those who are.