That's the point of Chesterton's fence analogy: Don't rip down the fence until you know why the fence was put up.
I think we're in agreement on this - if you don't have the tests, you don't know what the system does. The Michael Feathers approach is my favored path forward in these cases. Rewrites are more valuable in the small (class-level) than in the large (application-level) in the vast majority of cases. And if you absolutely need to replace an application (say, your company standardized on Oracle and Tcl and you can't hire any new developers because they laugh when you tell them your stack...) you do it piecemeal, building tests in your old system so that you can reliably replicate the functionality in a way that functions as a living, reliable spec.
I think we're in agreement on this - if you don't have the tests, you don't know what the system does. The Michael Feathers approach is my favored path forward in these cases. Rewrites are more valuable in the small (class-level) than in the large (application-level) in the vast majority of cases. And if you absolutely need to replace an application (say, your company standardized on Oracle and Tcl and you can't hire any new developers because they laugh when you tell them your stack...) you do it piecemeal, building tests in your old system so that you can reliably replicate the functionality in a way that functions as a living, reliable spec.
sigh