Granted at some GA ramps security can seem lax or non-existent. But we've always been a low-key operation. Where I work if you don't know the tail number of the aircraft and are not expected. Then you're not getting on. Also we don't let people onto the ramp until their aircraft is there.
Besides I don't want TSA at my side of the airport. Those FBO's that do are a joke and just make my job that much harder.