Better answer: we've been doing it so long that it's just kinda part of human existence. It's not great for you but I've also had sex with a fair amount of guys that keep their hands on their dick while watching women that don't even look human so much they they've busted their nerve endings and struggle to cum in a real vagina. Doesn't mean masturbation or porn is good or bad for you but both are sure as hell things humans have been doing for millennia. Humans also really love to gamble, eat fast food, and get on social media. Stop shitting on the behaviors of the human individual, guillotine the 1%, prevent corporations from owning real estate, tax any individuals' third property at 100% annually and exponentially for every property more than that, make it illegal to work without minimum wage even as punishment for a crime, and remind the 5% that it's their job to pay for bread, circuses, and thirdspaces. That's 90% of modern problems fixed right there.