No, it really IS a good idea.
If they tell him that he HAS to go to rehab, and he is not ready, he will simply go through the motions and not get anything out of it.
If he gets into trouble, that's his problem. Maybe he will get sick of getting into trouble. If he can't find a job, again, that is his problem. Maybe he will make the connection that job + no drugs = money = stability. If he gets a job, good for him. Let him figure out a way to get there and back. If he loses it, it's his problem. let him find another one. If he keeps screwing up, he will eventually get sick and tired of being sick and tired, and he will seek help.
But not a moment before.
You absolutely have to let this go. He cannot come home. Get it in your mind that he cannot come home ever again. If he surprises you and gets help and stays clean somewhere down the line, you can revisit the question as to whether he can return to your home. Hopefully, he will get himself stable and not need to come home.
If you let him come home, he could die. Because he will not stay clean at your house.