This is fine if the user was empowered to re-sign it after the mucking. The problem is that the user is rarely in charge of their own computer anymore.
Outside of mobile operating systems, eg on Linux, Windows and MacOS (and all the BSDs etc) it's fairly trivial to run binaries you built yourself.
But: re-signing is an extra step that someone who's just starting out and mucking around with a hexeditor might not know how to do nor even be aware of.
