I suspect the upstream concern was dealing with services that themselves like to spawn process groups. There's no hierarchy of process groups, once you call se

I suspect the upstream concern was dealing with services that themselves like to spawn process groups. There's no hierarchy of process groups, once you call setpgid() you've escaped the sandbox and the API can't help your parents manage you anymore. The use case in question is a build system that by its nature needs to deal with foreign software. Also FWIW, you could freeze a cgroup atomically in the very earliest versions and deconstruct it at leisure. You just didn't do it by sending signals.