The point is people who don't approve of any amount of illegal drug use aren't making that decision based on logic or science. They're making it out of an adherence to the law for its sake alone. Most people are fine with drug use to an extent, they just don't think about it. I'm totally fine with people who have consistent rules about drug use, but I think it's dumb when people stop thinking where the law begins.

The law is a malleable thing, and it should follow what is best practice based on science and statistics, not just what someone did because it was politically convenient. Marijuana, for example, is controlled as strongly as it is mostly because hippies were using it and it was easy to target them by targeting this drug, not because it's particularly harmful or dangerous.