There are no good drugs or bad drugs, in my opinion. There are drugs, and we can have a good or bad relationship with them. The only reason you'd have a bad relationship with drugs is if you can't use them safely. In this case, it's illegal to use them at all, so people sell them illegally and irresponsibly, and so it affects people's health. If marijuana was legal and could be sold responsibly, it would be a lot less dangerous.
If caffeine was illegalized, people with caffeine addictions wouldn't be able to buy it responsibly. They could only buy potent extracts of caffeine and they wouldn't know how much caffeine is in that extract, and then caffeine would be a lot more dangerous.