For your bareword file handles example, does "I can safely use this bareword filehandle because I know I haven't used it anywhere else, and I'm sure that no module I've used uses this filehandle either because I've read them and made sure" capture the process?
Don't be silly. A module using FOO as a bareword filehandle introduces no problems for me when I've used FOO as a bareword filehandle. Not even two modules each separately using FOO as a bareword filehandle causes a problem. *main::FOO is not the same as *Ancient::Module::FOO nor as *Modern::NonConformist::FOO.
And "I haven't used it anywhere else" isn't even good enough of a test. The test is much more like: I won't be calling this bit of code that opens bareword filehandle FOO again until after I no longer need access to the prior file I opened.
I'll be quite impressed if you can manage to get Perl::Critic to perform that test accurately.