Windows was still human when Mac torched him

Ok, so.

He was contaminated from his injuries. Nothing they could do for him. Better to put him out of his misery than let him suffer.

Wrong. Windows had been infected beyond any hope of being saved. Mac was defending himself and the others.

Well he also shot Clark in the face, and he for sure was human. So now he's got a body count. Not to mention, MacReady was a Vietnam vet so who knows what he did before The Thing.

And yet Apple grew to become the most valued company ever.

So what? He saved you didnt he?

there’s a theory that the thing can only assimilate by absorbing other organisms, not “infecting”. So Windows might very well have been burned to death for no reason. Damn

Serial killers do it for some kind of pleasure. Mac was justified, since Windows was being transformed into a Thing.