I've known plenty of people who have done coke... I have never seen one "ruin his life" to be honest.
Hence the line. I am very liberal with the drugs I'll put in my body, but I always do it sparingly and am cognizant of those respected lines.
For me, it's very easy not to slip into a rut. I'm sure I could shoot heroin and not get addicted. But some people don't even have this on their mind. Before the thought of substance abuse even enters their mind they're so far gone. Cocaine is a drug where this can occur. Stims are notorious for this. They're an all around ugly class of drugs which I don't really care for.
I haven't seen coke absolutely demolish anyone's life personally (I don't associate myself with losers that'd slip that fast), but I've seen it cause a myriad of unexpected, unwanted complications very easily. It just happens when you're around these drugs. Crack drama. I cut that out of my life years ago.