Quora itself is a good place for seeking sensible answers or information (that is why this question is here, 🙂 However it is constrained by question-answer format, which means you cannot have to-and-fro discussion between a group of people here.
We often find such discussions happening on Facebook, however they are few and far-between as Facebook’s stated (and generally accepted) positioning is that it is for staying in touch with Friends and family.
Zammrs: Social platform for public discussions and sharing of ideas is one such platform that has recently come up on the exclusive premise that people have opinions on various issues and they would love to have their views reach a wider audience. It simulates the socio-cultural norms regarding public-discussions and has a trendy UI. Zammrs also uses ‘gamification approach’ to assign Influence-scroes based upon user activities and how they impact other users.
Twitter was originally meant for to-and-fro communication but its innovative gimmick (140 characters limit) unfortunately put paid to that idea and it has evolved as a place for witty one-liners. Most of the posts there are by brands or by people promoting / building their own brands.