Doesn't the government try to ban heroin?? You have to live in the real world, not your ideal world, and in the real world people are not perfectly rational agents. They make mistakes. Each and every mistake could have been avoided if the individual just had a stronger will, was a little smarter, a little more prudent, or took a little more time to think, but just because mistakes can be avoided and some people are better at avoiding them than others does not change the fundamental issue: drugs, tobacco, gambling, and TikTok are trying to increase the rate at which mistakes are made. Wouldn't you rather live in a society where they aren't out to get you?

I think there's an argument that can be made, like, "well maybe 10% of the time people consuming alcohol is a mistake, but I just use it recreationally. The government shouldn't prohibit all drinking!" And sure. If it is really the case that people would take the same actions even if they had more time to think things through and were in a good mental state, the government should probably not be intervening for the 10% of the cases that doesn't hold. But you have to draw the line somewhere.