You are correct, but also overestimate how rational young&desperate perceive these self-destructing habits. It's far more emotional, desire to give big FU to all adults and their rules, and not giving a slightest damn about consequences on one's body.

When you're 15, you don't care how your life will look like when you are 30. It feels like talking about retirement.

God I am glad this period is long over, life can be so good now (and apart from alcohol, a bit of weed and few spectacular mushroom trips I didn't do any other substance).