It's reasonable & appropriate for the desk to ask for a credit card to cover incidentals, since they don't have your info. But the wording you describe is outrageous. PL users are already subject to abuse from some hotels. I've been in quite a few rooms through PL that are probably hard to sell otherwise - small, by the ice machine or elevator, no window, etc. But I'm not aware of reports that PL users are unruly. I think you just got a dumb hotelier.