I'm not sure how you can make this statement with a straight face. Name another site with tens of thousands of active users having this level of discussion without karma.
(the fact that you're not being downvoted for making such an egregiously incorrect statement is proof if it was needed that the groupthink is not so bad, btw)
Tens of thousands of users I don't know, but Lambda the Ultimate for example. Discussion on blog posts also generally has less groupthink.
Voting was intended as upvote means good comment and downvote means bad comment, but people use it as upvote means "I agree" and downvote means "I disagree". Not everyone of course, but a lot of people do. This problem is less severe on hacker news than on reddit, but on reddit more people keep posting regardless of downvotes whereas here they are banned from the site.
LtU has a decent community because it covers relatively esoteric stuff, and excludes a general audience by design. HN, on its worst days, is a glorified comments section for tech industry blogs.
