Naive question what are the non-nefarious requirements of being able to do this? I get that people have used it to work around things (for good and ill) but what’s the vanilla answer?
Unfortunately we don't use this all the time because some Kubernetes unit tests started failing when we first added this protection (the size of the binary is added to the memory usage of each container which caused some Kubernetes unit tests to use more memory than they did before). Ironically this exact protection would've protected us from Dirty COW and other such bugs but it's disabled by default (instead we make a temporary read-only bind-mount that we then exec which is slightly less safe but doesn't add ~10MB to every containers' memory usage).
But the actual answer to your question is that this was not originally intended behaviour (when we mentioned we were doing this to the mm and fs folks they weren't happy) and there have been patches posted recently to make this feature something you have to explicitly opt-in to.