Some people choose to live life differently from that of ourselves. This goes for children, adults, and people in general. Sometimes this doesn't always leave a lot of room for compromise especially if it is a loved one that chooses a different path. Like every path, it is composed of choice, both positive and negative. Some people choose to live honest good lives and some people choose to be self destructive and confined to their own self will. Regardless, it is their choice and their decision to live the way they want.
What if you see someone's path headed for a dead end? Well you can at first bring this to their attention if they wish for your opinion. But after that, they are really on their own and the only thing you can do is let them discover consequence for themselves. Sometimes more action is required on your own part especially if their destructive behavior begins to affect your personal well being. In this instance you have two choices, either participate or not.
Perhaps it is considered easier to participate being that you don't have to address the conflict head on. Many people choose this way of thinking and suffer the emotional turmoil that comes along with it. We can't always have our hands on the strings of another's life, keeping them from falling to the ground. Sometimes that very behavior in itself prolongs our loved ones agony, because they never reach their bottom, and never recognize their mistake.
Choosing to not participate is a very difficult task, one that requires great strength and adamancy. You have to first address the issue to the person affecting you, address their behavior, and then address the action that you are going to take for yourself. Everyone has boundaries, but it is up to us to express them to the person that has crossed them. Nobody is a mind reader and for even those that are, our interpretations can be misinterpreted. Say what you mean and as a follow up, follow through with what you say. This may be very difficult, especially if it means not contacting the person.
But in some instances this is the best way to give someone the space they need to really see for themselves where they are going and what type of lives they are living. Some will "see" and others will spiral down into the life choices they made. What is important here though is that you protected your "self" and your "well being" from being affected by their destructive path and behavior. It doesn't mean you have to love them any less, it just means that you are loving them at a safe distance.