There are many other activities that pose these same risks, so why are drugs a special case? These potential negative consequences are far from universal; what sets use of certain substances apart? Is it perhaps that they are seemingly easier to regulate than other potentially self-destructive activities?
Destroy yourself all you want buddy. My concern is when you snort your coke and put OTHERS at risk. Hard drugs take away your ability to act responsibly, to reason, and to be able to choose to stop using the substance. You have no right to do this on public property, nor your own, because there is no way to fence in the possible effects and inevitable effects.