There is a payoff from all of the bad things we do, otherwise we wouldn't do them. When life suffocates me, chocolate cake helps. So does sex or booze, but I am trying to make choices that lessen my next day suffering. Binging on cake brings on a quick euphoric bliss-like state that is just enough to make life tolerable again. Yoga and massages and a vast amount of other things work, too, but I'm a crackhead and choose the path of no resistance. Cake makes me not want to kill people, so I consider my eating it a public service.
I don't care if it's alcohol, crappy food, or shmucky guys, not a thing any of us can do will help someone stop making bad choices if that is what they want to do. It is hard enough to intervene on our own behalf. I own my brain, but I STILL can't control it and make it want to do the right thing all the time. I have zero control over other people, and neither do you.
Yes, you can try talking sense into someone, but after awhile, you will need to let it go. Love them for who they are in spite of their weaknesses, and love them for their humanity. If, however, what they are doing is killing them or they are a serial killer, you need to set some boundaries. Say I love you, but I am not going to watch you do this. Godspeed.
Unless they are a serial killer. Then you need to call the cops.