Earlier quoted context omitted.
Except it generally worked for gambling for a very very long time. The existence of a black market does not mean something should be legal. Human trafficking happens, but that doesn't mean we should legalize and tax it. (extreme example I realize, but I use it to illustrate a point)
Pushing it to black markets takes away the possibility of heavy regulation (which absolutely should be in place), and stigmatises victims (gamblers), making it harder to come clean to friends and family. I agree with your assesment that no one should even start to gamble, I just doubt that declaring it illegal will achieve that.
"Prediction market" ads running constantly on both sports channels/websites like ESPN. Shortly followed by mainstream cable news like CNN featuring Polymarket stats as a routine part of their horserace polling coverage. Gambling is now an omnipresent temptation for anyone even casually interested in following sports/political news.
And now millions of young men who previously would have had to seek out niche illegal venues to gamble have several dozen different apps on their phone offering to light their disposable income on fire by clicking a couple buttons every paycheck.