I understand that 98+% of readers may well have no problem with "impact" as a transitive verb,* and that many think the rest of us are just being diction snobs. At least for me, though, it's like some kind of allergen. I read it, and my face winces up like someone shoved lemon wedge in my mouth. And, as is the way with many allergens, I appear to be incapable of building up a tolerance to it.
My usual method of pointing this out to students who would have me read their work is to circle it and offer some friendly-toned little comment. Empirically, however, this has had zero effect on the probability of students using impact, v. trans in subsequent papers I am asked to read. For repeat cases, I think now I might try buying a pen whose ink is the color of dried blood and scrawling "YOU HURT ME EACH AND EVERY TIME YOU DO THIS" in maniacal looping cursive instead.
* Hypothetical examples: "I wonder how Jeremy's little rants about ASA impact his career prospects" or "I wonder how the more inane anonymous commenters on Jeremy's blog impact his mental health."