Rewrites are only cheap if the rewrite solves the problem. And the rewrite can only reliably solve the problem if you understand the problem, and even then it'

Rewrites are only cheap if the rewrite solves the problem. And the rewrite can only reliably solve the problem if you understand the problem, and even then it's obviously not a guarantee. If you have a huge blob of code that nobody understands then re-generating a new blob of code that nobody understands is unlikely to solve the problem. That said: I've always been a fan of optimistic rather than pessimistic merging, at least for human-generated code.