“””If someone can explain why I’m wrong here, I’m open to alternative opinions.”””
You would first have to overcome decades of teaching that only cops are qualified to handle criminals.
Nothing having to do with the police would be coming to my mind.
I would consider myself dead already. I would try to see if I could deflect the gun to let others in and take they guy out.
I would also like to see legislation what would exonerate anyone killing the perp on the spot.
Any animal pulling a stunt like this should know up front they won’t leave the train car breathing.