That's the trouble with some warnings: some instances you want to fix and some you know you can safely ignore. I presumed that we were aiming to turn this warning on permanently, but that may not be the intention, and maybe the downside you highlight makes doing so not worthwhile.
Turning on -Wsign-compare may be useful, but I don't think combining it with -Werror is. This is the trouble with warnings in general: they may or may not point out a real bug. Fixing the bugs is useful, but fixing non-bugs really isn't, unless the code is somehow improved as a result. Making code look worse to remove a warning is clearly not useful. --Juan