Tins,
Since when is showing one's friends your aircraft not a valid reason?
Since I am talking about relatively large public transport airports here, I actually find it sensible that they would want to restrict access to a controlled
and dangerous work area. Primarily it is not about "terrorism" or any of that bollocks, but about safety and efficiency.
Some time ago I was talking to the policeman who controls crew access airside (a proper police officer with real training and authority, and yes, we do usually have separate crew channels in the continent), and he was telling me about the number of spotters who try to sneak in to get a nice pic (fair enough) and end up wandering into dangerous areas and placing themselves at risk. This guy was very pragmatic about it, and genuinely concerned with everyone's wellbeing rather than some nonsense "security" regulation. Mind you, he'd been working there for the last 20 years, so not exactly clueless.