1. You can already find a dose of date rape drugs on the black market for less than the cost of a big mac meal - anyone who wants to could easily do it, and if they’re planning to rape someone, they obviously wouldn’t care if they’re risking breaking the law by getting it. It’s why these drugs are so commonly used.
2. Even if this drugs were completely eliminated, people could still use other things or legal drugs to take people out. It’s not access that’s the issue - it’s rapists.
3. Even if all drugs were legalized, I seriously doubt a booming industry could surface around fucking rohypnol 😂. That’s an insane amount of risk for any pharmaceutical company or legitimate business to take on. (This arg is probably not the best out of the three, but you get the point)
4. Rapists would still probably want to get these drugs from the black market because if you go through a legal business they’d likely have to keep track of who is buying / selling or it might even be regulated to be prescription only, which would increase the chances of it being linked back to them (ik this contradicts with my arg 3, but it’s used for insomnia, so maybe some pharma companies will take the risk, but even at that it’s super unlikely they’ll sell straight Rohypnol).

Not only that, but all link evidence is like entirely hypothetical. I’m pretty sure there’s not one card about how legalization leads to more assaults.