Sometimes, friends end up in bad crowds. Sometimes they end up befriending bad people who they believe "aren't that bad". Then you go meet all their junkie buddies, and next thing you know, your house is getting robbed because the local methheads now know where you live. Issue isn't just what happens when your friend's there, but also painting a target on your back by making yourself known to dangerous people who hate you. It'd be like insisting an lgbt friend come to the local church meetup and saying "well yeah, sometimes they talk about how all of those dang queers are trying to convert their kids to devil worshippers, but they're not so bad once you get to know them!" Exposing yourself to people who hate you and openly fantasize about wanting to murder you is always a stupid idea.