Sir, if I preoperly recall, that's exactly how you discard premises. Taking a premise and applying it to a more extreme situation just battletests it. It's done in justice and law courses, etc.

"If the common good justifies killing X agent, then it must be ok for a doctor to kill a patient in their sleep, take his organs and save three people with his two kidneys and heart."

Also, what Yale did wasn't right, and the students just defend themselves... If, for example, you were robbed wouldn't you care? "Oh but there are thousands more people poorer than me, I shouldn't bother".