It's less that humanity is awful but more that there is people who benefit from everyone below them in power being miserable and worn down
Fight with your fellow man, not against them because the powerful have it the easiest when we are divided
The teen years are the angsty edgelord years where you hate everything, you do get a more positive outlook on life (aka giving less of a shit what others do) when you get older.
Nah there are still adults who complain a lot about how other people act, and there are adults who see their life as miserable and complain about it a lot