Losing the magic

Doesn't look that way to me. Compiler developers already acquiesced to these demands and provided flag which makes clang and gcc to make signed integers behave that way.

Now you arguing about different thing: “right to be ignorant”. You don't want to use flag, you don't want to use provided functions, you don't want to accept anything but complete surrender from guys who have never promised you that your approach would work in the first place (because it's not guaranteed to work even in C90 and gcc 2.95 from last century already assumes you write correct code and don't overflow signed integers).

And that's precisely the problem. You ask for common sense but neither computers nor compilers have it.

They couldn't employ common sense during the optimisation because it's not possible to formally describe what “common sense” means!

Thus they use the best next substitute: list of logical rules collected in the C standard.

That's how specification is changed and how new switches are added. People employ their common sense and discuss things and arrive at some set of rules.

Similarly to how law is produced: people start with common sense, but common sense is different for different people thus we end up with certain set of rules which some people like, some people don't like, but all have to follow.

Only with C standard situation is both simpler and more complicated: subject matter is much more limited, but agent which does the interpretation doesn't have even vestigial amounts of common sense (law assumes that where there are contradictions or ambiguities judge would use common sense, C language specification writers have no such luxury) thus you have to make specification as rigid and strict as possible.