1) Social pressure: the community must evolve in such a way that its members as a whole frown upon negativity. Hard, because it takes time and can go wrong. Or,
2) Moderation: a group of members you trust is tasked with actively deleting useless comments and threads and banning useless contributors. A zero-tolerance policy for stupidity. Is that elitist? Maybe. But an elite community is hard to grow when idiots are tolerated.
There is literally no way to engineer away jerks. A social problem requires a social solution.