It's a great question. I also would love to unearth an intelligent community where discourse isn't limited to growth hacking, jQuery plugins, and startup pivoting. HN is the closet I get, but people here tend not to take intellectual risks and experiment with creating new thought paradigms.
Don't get me wrong, there are some tremendously bright people here who I learn a lot from. but the Reddit-esque social dynamics (ie, karma, hivemind,) tend to put safety pads on anything remotely radical or risky discussed here. Quora can actually have some pretty interesting content, but, again, there's similar reputation management going on that prevents discourse from elevating to being somewhat interesting and important.
Also, the social dynamics here are not fixed. They can and do change over time. It is possible to participate with an eye towards fostering change of a sort you would like to see.
Don't get me wrong, there are some tremendously bright people here who I learn a lot from. but the Reddit-esque social dynamics (ie, karma, hivemind,) tend to put safety pads on anything remotely radical or risky discussed here. Quora can actually have some pretty interesting content, but, again, there's similar reputation management going on that prevents discourse from elevating to being somewhat interesting and important.