Airspace constraints in and around GAAP zones ( e.g abutting Class C airspace in alot of cases) would require certain dispensations to convert them to Class D control zones, otherwise the demise of GA at those airports would be a matter of when not if.
Dispensations such as :
-a reduction in met minima to allow for continued flow of traffic into and out of the CTR during times approaching marginal VMC.
-Differing sep standards being applied to aircraft operating within the CTR, i.e IFR treated as VFR. - try applying 1000ft sep IFR to IFR when the vertical limit of the zone is 1500ft
-Anticipation of runway standards so as to allow for efficient movement of traffic.
These are just to name a few. If you put these into place in a Calss D environment you would have, um..., hang on.... GAAP.
GAAP zones used to effectively be Class D CTR's. It was realised that something needed to be done to improve the system to cater for the increasing numbers of aircraft movements and operations, hence GAAP was born.
GAAP works.
It is the very small minority who enter the zone at the wrong altitude, who dont have any sense of airmanship whatsoever, who cant follow to save their lives, that puts doubts and pressure on the system. Instead of penalising the good pilots and operators CASA should do their job as regulator and crack down on the few instructors and students who cause GAAP zones to be unneccesarily hazardous.
Rant over.