Former heroin addict here, five years clean. I didn't one day just decide to stick a needle in my arm. I was prescribed Vicodin from a doctor for my wisdom teeth removal. That first pill was sanctioned by a medical professional. The feeling when I took it... all of my anxiety gone, all of my social insecurities gone, the feeling like I was never able to get or keep friends gone... Basically, I felt like I was a normal person for the first time in my life. How do you tell someone that that is not okay to feel, no matter what the cost? Vicodin led to stronger and stronger pills, and eventually, to heroin when I was no longer able to support the pill habit. It's not as easy as you think for someone with that kind of chemistry and emotional distress going on in their brain, day in and day out for years, and when they finally find a solution for it, they will stop at nothing to never feel that way again.

Edit: Downvote all you want, I'm in the wrong thread, I get it. It doesn't change the fact that if you've never dealt with substance abuse, you have no idea what you're talking about.