Dan Todman at Trench Fever has a chilling (but hopefully not serious) post about about plagiarism.
In 1641, William Ward, a Catholic priest, was executed in London:
"He hanged till he was dead for he was ript whilst he did hang & being cut downe his members being cut off & cast into the fire, the Executioner ript him up and tooke his heart & threwe it into the fire which lept out againe & no man toucht it till the Executioner a goodwhile after threwe it in againe, his head and quarters were brought backe to Newgate & boyled & are to be set upon 4 gates of the Citty. "
Anybody who could inflict this sort of suffering and despoliation on another human being was plainly motivated by enormous passion, anger and fear. Yet most historians would consider this too light a punishment for those found guilty of plagiarism.
I agree that plagiarism should be punished swiftly and without exceptions. However, I am willing to stop at failing the student and maybe expelling them instead. This is a nice post with a good explanation of what plagiarism is and why others are outraged by it.