I don't pretend that that is what most people are thinking when they encounter the problem, but the "unusualness" of pushing someone off a bridge is certainly affecting their intuition, and so concerns about stability probably play a role.

I don't know, lot of people talk about how he's "not involved" or "innocent" or how you should involve people who aren't already part of the problem - it's the same as the one with the guy with healthy organs and the dying transplant patients.