As an adult he certainly has the right to make his own choices. I do think acting like a lunatic (not just an average run of the mill drug abuser) is something that is hurting his children, which is wrong in my opinion. As long as you are not hurting anyone (pissing someone off is different), and you're an adult, do what you're gonna do...do what makes you happy...and do it with other consenting adults.
Regardless of anyone's right to make decisions about how they live choose to their lives, being human and having compassion, makes it hard to watch someone fall apart, whether they are choosing that road or not. If you can't not judge, you just have to not watch. That's typically my personal strategy.