Ask HN: Why are subreddits so toxic?

Has reddit always been so toxic? Should subreddit moderators have stricter codes of conduct, especially those that are more "industry/tech/profession" oriented? I'm from the "tech" industry, and I was surprised to see that tech subreddits are also fairly _arbitrarily_ toxic instead of the negging-but-constructive type comments that pass on HN.

Or is that entire idea just against reddit? HN is a more moderator based forum, for example.

What are your thoughts on community censorship? When do things cross a line? Or should it just be a subreddit owner/moderator based thing and let everyone just figure it out...