If I had my own young children living in my home I wouldn't be able to invite the person to stay with me. If I lived alone I might consider it on a very, very, short-term basis; but I wouldn't be comfortable with it for a number of reasons,
I understand that some people make the foolish choice to use drugs when they're young, and then things get out of control. I think about the fact that someone is someone else's grown son or daughter who got in too deep, and I hate to imagine someone's son or daughter living on the streets. On the other hand, I ask myself if I'd like to see one my own kids taking in someone with that particular problem, and I'd be really worried about them for a number of reasons if they did.
It's not an easy question to answer, but I suppose - provided I didn't have my own kids living with me - I might consider taking the person in for a very short time, and aiming to see if I could help him/her find somewhere else to stay (and letting him/her know those were the terms up front) and/or get treatment and other help from someone other than me.
Something to think about, too, is whether the person has a drug problem with something like his own prescription medications or other legal stuff, or whether his problem is with out-and-out illegal drugs that he isn't going to be buying at the local CVS.
If criminal background, criminal "pals", and illegal drugs were involved I think I'd have to put my friend in touch with whoever I could come up who might be able to provide him some help and hope they could help him. Really, when it comes down to it, friends and/or family members aren't really equipped/qualified to help someone with that kind of problem. I couldn't entirely "turn a blind eye", though. I'd have to keep paying attention to where he was, whether he had been in touch with anyone who could offer temporary shelter and/or help, etc. It is possible to stay in touch, let someone know he's got someone who cares, and yet limit how much he is allowed to become a major part of one's day-to-day life.
You used the phrase, "open my home". I don't really think people who have children are ever wise to "open their home". Homes provide a certain type of security, shelter, and shielding from some of what goes on outside the family and some of the people outside the family. When all is said and done, I think people's first responsibility to preserve what home can offer to their own children. Anyone else has to come second. :/