On the flip side, all threat of consequences works as a deterrent only when there's the expectation to be caught and punished.
By always catching but never handing out punishment to kids violating rules, you only teach them that consequences are inconsequential.
Your thoughts are valid and I agree – in principle.
The proportionate punishment does, however, depend on the severity of the violation. In an academic context, there are few things as severe as blatant plagiarism. Being caught in not just cheating but brazenly copy-pasting other people's work can imho be appropriately punished with expulsion, be it in the US or elsewhere.