@Waifuhunter101 He doesn't hunt them down, but he also doesn't overlook them, when they throw deadly intentions at him, killing intent is a death sentence.
If the guy introduces himself as a mage, the correct thing to do is shut him up if he starts working himself into a rant, that's how they hide their spells. Just spin a ton of words, with their magic hidden behind bullshit.
Why not just tell him he already killed the demon in the barrier? He's been watching him use the instant kill technique down half the tower, so he should believe it...maybe.
@CountryMage That probably depends on the setting. Some of them, every single word would become part of the incantation and a long ass rant like this would have wildly unpredictable results if any magic actually went off as a result of it.
Anyway, with the way the MC's abilities work he pretty much just killed the guy the second he began to direct ill intent at them. He could have just killed the dude's tongue to silence him, but perhaps magic here can be cast silently. Most effective crowd control is death.