It was meant to highlight russellbeattie's propositional logic ("if it kills someone" then "it's still your fault"). I agree with you that it's "not terribly dangerous"[1]. Your comment seemed to have omitted the premise, so I wanted highlight how it was a non-empty set. [2]

[1] It's also not terribly dangerous to drive without a seat belt on either. I don't advise people do so.

[2] "Firing a bullet into the air" does not mean it must have time to slow to terminal velocity, nor is a bullet hitting a body the only way to kill. (See "Twenty-three people were electrocuted after celebratory gunfire brought down a power cable".)

However, with any significant angle off-vertical, the bullet still travels in a stable trajectory and orientation, so will impact with a speed much higher than random-orientation terminal velocity, and be potentially lethal, even if passing through some roofing material on the way into your body.

So yeah, don't shoot into the air, and don't be around where anyone does...