Yes. It's a parent's responsibility to teach their kids about the risks of drugs.

It's not everyone-else-in-the-world's responsibility to avoid building marketplaces where anyone can transact freely with anyone else.

Most 11yos don't have access to hard drugs. This significantly lowers the barriers to access for a tech savvy child or teenager, who is not equipped to properly evaluate the various risks in either the transaction or the drug itself. Many parents will not understand these markets and their kids will. It is obviously not directly responsible for anyone's actions but it changes the landscape considerably, and puts a finger on the scale of underage drug use.