I have one question, have you ever been addicted and had to quit? Because, it doesn't sound like it; and the way you put your opinion seems overly simplified.
As "easy" as it is to quit, there's a lot more to it than just stopping. I can personally say it's a tough road, that some people can't handle mentally. Then you have the case, with some drugs, of the body building a dependency on the drug. It becomes not only mental, but physical. If they don't get their fix they can have severe reactions.
I'll agree that the person has to truly want to change for it to work; however, it's not something to take lightly (which is the tone I got from your post). Everything we do is a choice. We all must face the good and the bad. Those that choose to find the jagged path back to good have a better understanding of the hell some people go through. It may be sympathy on my part; however, it's a lot easier to help other people when you care more than to just say "Quit" and realize there's more to it than that.