"If it happens a second time, with another student, it's not the students."
I would have to disagree with this. It's muscle memory that keeps the finger indexed and the gun under control. Students just don't have that yet. They're thinking about the million other bits of information that we, as instructors, take for granted. I could stomp on the offender as hard as possible, making an example. And two minutes later someone else will sweep because he dropped a magazine. I see 10 year USPSA Master shooters sweep the crowd. Handle a firearm enough and we all do it. The best instructor, following the most conservative of lesson plans, will still get more than one sweeper.
"Consider this list of facts:
They can do anything we teach them to do.
They will do anything we teach them to do.
They're doing something wrong."
I wouldn't call them "facts."
Not every student can do what we teach them, exactly as we teach it. Most people have smaller hands than I do. They can't physically manipulate the gun like I do.
They can only take what we teach them and apply it to the knowledge they gain from other instructors. I don't want clones of me, I would hope that they would end up better shooters.
Students aren't the only ones who make mistakes on the line, instructors get tired, distracted, complacent, bored, etc. because we're human.