We have two crowds shouting their messages ("masturbation is completely safe and healthy, no bad side effects ever", "porn is a dopamine addiction to superstimulus and will destroy your mind"), both of them claim to have science on their side, and imagining the world where both are correct does not make much sense.

Really? I can imagine a world where plenty of things that might be considered addictive are quite safe and healthy, as long as you do them in moderation - and what counts as "moderation" may well be different among different people. E.g. some people might be highly sensitive to addiction, so that their only alternative is quitting the habit entirely.