If you hadn't gone to his parents and if something should happen to him and his parents find out that you knew and could've prevented it you would be blamed and feel like a horrible friend.

On the other hand, it really depends on the maturity level of a person, if the person is mature and you talk to the him and explain how his actions may be hurting his parents, and those who live in a conservative society understand that, then he would think about it rationally and accept it. But if the person is still juvenile then they may ignore whatever you have to say or even retaliate and in this case, if his actions would lead to more harm in the future, you may choose to go to higher authority i.e. parents, and parents can also handle it in such a way such that he may never know that you told on him. And yes it may be beneficial for him in the future.

I have a friend that was in the same situation that your in and by the way she handled it, and even though her friend got upset over it, things turned out fine. Hopefully they'll turn out fine for you too.