Why else? Perhaps you mean that drugs physically harm you, like you will become a methhead or crackhead with your teeth falling out etc? But that requires really sliding down the deep end...
Perhaps I was raised differently. As a kid, my parents told me upfront that drugs are awesome and people do them because they are really enjoyable not because junkies are evil mutant monsters who like to destroy their lives, and that the awesomeness is the danger in them, that they are empty enjoyment without deeper achievements etc.
This was in contrast to school finger wagging lectures, which just said that drugs are baaad and you must learn to say NO or you will destroy your health and life and drugs are poison and terrible and will eat your flesh (slides showing the effects of krokodil, and shady people in alleyways). Which just confused me because why such a big deal about poison that destroys your life? Why would anyone do this if it's so straightforwardly bad?
In the other hand, you also have a feeling of this person not being a productive member of society. My tax dollars go to fixing this persons' mistakes. I wouldn't complain if my tax dollars went to properly rehabilitating these people though.
It is a chicken and egg problem though, like many others in life. Do people take drugs and therefore stop progressing in life or do they not see any other paths forward, any positive examples to follow (for whatever reason) and therefore turn to drugs, and it's perhaps one bad decision they can take out of lots of bad options from the cards they were dealt?
People rarely ruin their lives if they just experiment with drugs for recreation, self-discovery, psychedelic trips etc. if their life is in order, with healthy relationships, a pride in their work etc. The danger is mostly when it is a substitute for life/social achievements.
Similarly with porn and OnlyFans. It provides an intimacy to people who don't currently have the means/skills to get it in real life. But could they perhaps develop it if they put in more effort? Now the bitter kind of people would say it's not worth it, they will just cheat on you, trap you in marriage, the divorce you and take it, everyone is a golddigger or just wants to date assholes etc. etc. There's lots of ideologies for this. Again chicken and egg. Are you unable to form relationships because you spend so much time with fake intimacy, fake achievements in video games, fake virtue and validation on social media etc, or the other way around?
The underlying issues are societal and they aren't just about the surface level products and services.
It's common, at least in my bubble.
But there's lot of sneering like this https://9gag.com/gag/arVYxm5 spreading on social media, which is essentially that girls on onlyfans are going for the easy money instead of more "decent" work and career path. I know it's just a meme, I'm not defending a silly image as truth, just as the illustration of the viewpoint. The idea that there is a who-deserves-what aspect.
And perhaps you think the anti-porn Christians simply tell boys not to jerk it because of an irreducible argument that "Jesus doesn't like that", but to me it's pretty clear that there is a deeper Christian pattern underlying it, namely suffering/effort giving rise to reward, and that it's immoral to sidestep that, Garden of Eden, Christ paying for sins by suffering on the cross etc. The protestant ideal of hard work etc. Do these ideas seem foreign to you?
While I can certainly imagine someone feeling this way, I've never thought this and I've never heard anyone express this perspective. I think you may be imagining too hard.