FF: you clearly don't fly for OŁT$ (or they've changed SOPs)!Pa28s slip fine, as indeed do Boeing airliners viz the Gimlet(?) Glider!
A full flap max slip in a 152 is possible (we all knew that didn't we) but I once had a little pitch instability in the form of a gentle nodding... The manual for 1980 models doesn't have a reference to 'no sideslips', only to minimum flap required during x-wind landings; flaps are not permitted during intentional spins due to excess airspeed fears during recovery not because of 'blanking' as a previous contributor implied.
Field in Sight: If true, your examiner was odd.
Slipping left or right makes no difference in my experience though witha left side pitot a slip to the right can produce slightly more fluctuation in the IAS ( I'm guessing due to turbulence off the Propwash), but fly attitude and there's really no problem; in any case initial student slipping practice often produces a nose drop and increasing airspeed!
So can we all agree: a. slipping is a good thing, b. most of the training fleet slips nicely (yes I know Ercoupes can't) and c. it can be useful in x-wind landings as Chuck says?