Well, first of all, it is bad taste because you just don't say something like that. He was trying to be funny and it wasn't. If you were in the position the teacher was in and had a gun pointing at you, you aren't going to think clearly. She did her duty as a teacher and protected the students, but that still wouldn't have stopped the shooter from looking in the closet and killing them. Ultimately, people on the internet love to troll because they think they're above it.

Okay, 'you just don't say something like that' is really a horrible reason. I mean, it really isn't a reason. It's like punching someone and then telling them 'because I could'. Meaningless. I'm not trying to be an asshole, I'm just saying that it's really got no substance behind it.

I don't think that was a troll. It's a perfectly valid statement. What are you trying to say when you point out that the shooter could still have looked into the closets? The point is that he didn't, because of the teacher's actions. Nobody (that is, among OP, the commenter, and myself) ever said that the teacher's actions were anything short of 'her duty as a teacher'--in fact, she went far beyond that and deserves to be recognised for it. I know that when you're in danger you may not think clearly, but the fact still remains that she put anyone in the gym in danger. Nobody is saying that she did so deliberately. I think we all recognise that.