If the GA was making people pay only for bags that did not fit in the sizer - that's completely fine by me. I've been on way too many flights over the years where people bring oversize carry ons, and its gotta stop somewhere. In fact, I think (flame suit on) that elites should also be forced to pay the checked bag fee if they have a non-compliant bag that comes to the gate and needs to be checked there. I'm also for more enforcement of the existing carry on dimensions.
Where I do have sympathy for the folks who were charged, and where their anger should probably lie - is with the luggage manufacturers. Truth is, when these folks were buying the bag, they were most likely sold a 22" "carry-on compliant" bag that actually isn't, because almost all manufacturers don't count the wheels/handles in their specs, while the airlines do. This game by the manufacturers has to stop - in fact, with the airlines getting more strict with their own bag rules, I'm a little surprised there hasn't been a lawsuit against a luggage manufacturer yet (at least that I've heard of). While not a fan of regulation in general, I think it would not be a bad thing to regulate how luggage manufacturers can market bag dimensions and some sort of carry-on complaint label.