So far I could not find any reasonable translation for "sledgehammer argument". Automatic translations spit out "argumento de mazo." However, everything indicates to me this is just one of those totally non-idiomatic automatic translations that make no sense.
Alternative English expressions from Wikipedia are: "thought-terminating cliché" (also known as a semantic stop-sign, a thought-stopper, bumper sticker logic, or cliché thinking)"