Religion, capitalism. Powerful groups want more people to have more children.

Luckily I’m in a progressive enough country that even in school we were taught that masturbation is a thing and not necessarily bad.

As for negative effects - if you do it TOO much, particularly with a very strong grip, then don’t be surprised if, when having actual intercourse, you’re just not feeling much and might be unable to reach orgasm. You might even be uninterested in your partner sexually. A few days without masturbation will fix it though, doesn’t seem to be permanent. Day 2 without doing it and I couldn’t keep my eyes (or hands) off my wife’s body.

Sex was very infrequent for me and my wife in the last few months of her pregnancy, so that’s how I know. Soon as we started doing it on a somewhat regular basis again, I opted to quit jerking it because I wanted to enjoy the real thing more, even if it’s not every single day. No long-term negative effects that I’ve noticed.