I find the argument against rewriting to be like the DRY principle: an oft-misapplied rule of thumb causing much of the unwarranted complexity in software around us.

Truth is, the cost of “just rewrite it” is as large as your unit of software architecture. Prefer loosely coupled, cohesive small parts and rewriting to accommodate changed requirements becomes preferable to the alternatives that tack on complexity as landscape evolves.

The world and our model of it both evolve all the time; the current version is not a work of an idiot but a necessary step towards a better solution and a lesson.