[aidenn0]

Indeed. My intuition based nothing other than my subjective experience is that there are times that throwing away the code is the correct decision, but they are a rounding error compared to the times that people want to throw away the code, so to a first order of approximation "never start over from scratch" is correct.

Simply shifting the burden of proof to the "rewrite" side is usually sufficient. Where I currently work a rewrite request is not answered with "no" but "show me the data." 90% of the time the requester doesn't even try to gather data, the other 10% of the time results in some useful metrics about a component that everyone agrees needs some TLC, whatever the final decision.