I think people believe that onani leads to looking at p0rn, which is inherently exploitative to those involved (men and women) and a foul industry. Likewise, it can produce exaggerated sexual fantasies that are unhealthy and can create predatory relationships.
It's hard to imagine jerking without explicit content, and once you have gone from Swimsuit edition to Softcore, it's hard to go back... From softcore to hardcore, it's hard to go back... From niche hardcore to regular, boring hardcore... It's hard to go back...
And it leads to becoming a person who does this frequently... And then, what if you want a family? Do you really want to be taht guy who is looking at crazy stuff and rubbing one out while your infant daughter is sleeping 30 feet away in her room? Do you want to be the guy whose wife is out of action from giving birth and you are like "Oh, OK, I will just look at explicit hardcore content and content myself..."
It's a bad habit.
It also creates crazy expectations of others which may even lead to so desiring some novel experience that you have an affair or "open" your marriage.
Nah man freedom of speech includes hate speech.
If "hate speech" must be banned, why even have a democracy..?
You have to have faith in the ability of people to discern right from wrong, and the very first test of that is whether people are going to be mentally hijacked by some guy saying the N word.
If you believe people can't do that... Why vote? You just support soft totalitarianism.