I don't think having rules is going to make a difference. People just need to suck less. Reddit has rules, and subreddits usually have their own rules, but you still get tons of jerks. People are absorbed in their own little worlds, especially the hateful ones. They forget they're interacting with other humans. Anyone who's ever worked retail knows what it feels like to have a customer just walk up yacking on their cell phone and not say hello as if you're just some machine, or in fast food, customers are notably more nastier in drive thru vs ones that come inside to order (because they don't see your face at first.) Also it's why they say when you're lying on the ground hurt/dying, that you should call out to someone specifically, and look them in eye and ask for help, because people are just so absorbed in themselves and assume someone else will help.
On YouTube, etc. you just see an extreme version of this self centeredness because they have total anonymity and they can just go on and say awful things with no real repercussion.