Cardiff Airport itself has a great area for watching aircraft and that is located southside of the airfield "Rhoose Flying Club". You can see most areas of the airport and is recognised by the airport with some management ocasionally taking their children down there and having a chat with the regulars about various things.
Although this great facility and other excellent viewing points exist you will still see families parking illegally near the perimiter fence on a roundabout either waving relatives off or just taking a look at the arriving aircraft. Several vehicles are supplied either with a summons or a ticket every year.
The regular enthusiasts on the other hand obide and respect the law as they do not wish to jepordise their hobby.
I totally understand why the police in general find enthusiasts as a useful weapon when it comes to their fight against crime as they are actually more likely to spot suspicious activity before the police or airport security will while on their patrols.
No my take on it is if the enthusiasts are not on private property without permission, are not causing a nuisance or damage then they should be left to do what they love doing. This is why the article which I brought to your attention at the beginning of this thread is such a shock.