Police entrap people all the time with fake hookers and drugs, and arrest them without a crime being committed. There are charges you can receive based on intent. Try telling a police occifer the seperate baggies of dope are personal use. Nope, intent to sell. It isn't right, but it happens (talking about the US). Usually sex offenders don't find their minor victims on the Internet (typically someone they know and encounter regularly), I still think it's doubtful a repeat offender would otherwise turn there specifically to meet minors, unless a shining opportunity resented itself. Of course, illicit chatting with a perceived minor is also illegal, but the girls they use to trap people aren't minors and therefore the people who show up with booze only intended to commit a crime and perceived that they were.
Drugs could easily be legalized globally. They were once legal, and it's likely in many places they will be legal and regulated again. I cite the alcohol prohibition period in the US.