AFAIK there isn't one and is not really an issue of platform or technology. In my opinion even if such a site were created it would devolve quickly into everyt

AFAIK there isn't one and is not really an issue of platform or technology. In my opinion even if such a site were created it would devolve quickly into everything negative that you mentioned unless it has a solid team of great moderators, architects and leaders that understand human nature thus designing around it. HN is an example of a well moderated site, but it is a simple site relatively speaking. Stack Overflow could be everything you desired but was not guided in that direction. From my experience editing posts on one of their groups it was expected to just grow organically without external intervention. I assume this was to make a big knowledge base platform with low overhead by outsourcing all editing to volunteers that would eventually be acquired for a nice sum of money. I expect some day people will need a paid account to access answers, but that is the cynical side of me. I have never seen a large complex site like SO designed with human nature factored in but would love to see one.