It’s fine, provided it’s not a plot hole - i.e. your fantasy setting needs to not have abolished blindness as a realistic malady, which some settings do. E.g. LOTR 100% has blind people, while the Harry Potter universe only has very poor blind people, since solving blindness is as trivial as a polyjuice potion, even if nothing else works (and something more effective is bound to work).

Banning specific guns is pure theater, even if it passes. There’s zero real safety in it.

I think you mean false premise or argument from false premises. “A, therefore B”, even though A is false.