Wouldn't it be good to prevent the shootings before they happen?
But this thread is about how the cure is often worse than the disease with prohibition. See: 18th Amendment, War on Drugs. Concocting a hypothetical scenario where the drug is Disney-villian evil and enforcement is not an unmitigated disaster is hardly a decisive rhetorical victory, wouldn't you say?
It _is_ a decisive rhetorical victory, even if you don't like it.
1) The scenario proposed seems...outlandish. I could argue for a host of provisions in law or the Constitution based on the possibility of widespread development of bulletproof skin, but I fail to see the utility of doing so.
2) Even within the hypothetical, it is possible (I would argue probable) that banning the evil rage drug would simply make the situation worse than alternative solutions, in which case the proposed amendment would be a positive.
Edit: You could argue that the above amendment is also ridiculously unlikely to pass and isn't worth debating either. You'd probably be right.
You could also easily just slap liability to the seller of known harmful substances (see the sibling to your comment) or enforce warning labels as on tobacco products (eg "this product makes you shoot people and shooting people will get your thrown in jail").