Violence, death wishes, bullying, insults, self-hate, lack of respect. If you're comparing 4chan and Reddit, then... I agree about Reddit, and my general feeling about this website is also that people overreact based on overinterpretations and buzzwords. Reddit isn't tolerant at all.
The brain needs a proper diet too. If you feed it content filled with hate, it will deteriorate your relationship with yourself and others. You're going to mimic what you've read and how others in a place you frequent relate to you. And you're going to ruminate pointless destructive insults and "opinions" that you've encountered. Ruminate instead of doing something that will propel you forward in the same time. There is no point in thinking repeatedly "I am a loser and degegerate, nobody likes me" (for instance). You are who you are and judging yourself harshly and inflicting psychological suffering on yourself isn't going to move your forward. Quite the opposite. With a lot of things success depends on whether you just keep on trying and moving forward and the major way you can sabotage yourself is not trying because you think you already lost the game.
How about reading other websites than 4chan and Reddit? I don't stay up to date with the English-speaking news websites, but there are plenty and maybe someone else can recommend something.