It's not rocket, it's rocket science. I.E. a complex or difficult mental exercise or field or study, used frequently in an ironic sense to suggest that a task should be easy or simple because it is not rocket science. (definition from wikipedia)
Why do people use this tired old cliche. Surely it's not heisenberg debugging to come up with something other than rocket science (or brain surgery?)
Because people don't know what "heisenberg debugging" (or whatever you use) is? After all, your primary objective is not to be original, but to be understood.
Right, it's a figurative expression for a reason. There's a balance where the listener/reader must understand the literal sense of the phrase to understanding the rhetorical meaning. If the listener/reader doesn't understand "heisenberg debugging" in any relevant context, they can't easily find the second meaning in the figure of speech. I'd go so far as arguing that figures of speech need to approach cliche entirely because of this necessity. It's not rocket science.
Point taken. What people should say is "it's easy" or "it's not difficult".
Continue with that line of reasoning very far at all and you'll be left with something that lacks any flavor or passion. Something very close to Newspeak.
What people should say is what they already say. English doesn't have a central authority, it's defined by common usage.