Similar situations have been discussed here.
Facts are, some dealers do more stereotyping of individuals than others.
That said, if I owned a dealership, I probably wouldn't let everybody that walked in take any car out. That's crazy.
I probably would let most people test drive a car WITH a saleman in the car, especially if it was high powered rear wheel drive.
When I was testing cars, the local Ford dealer let me take a couple of the Mustang V6 models out for as long as I wanted. When I asked to take the GT, he came along with my wife and me. Funny watching this guy wedge himself in that back seat! Now I'm 52, and not so much of a crazy threat anymore, but he told me they someone pull out from the dealership in a GT, got sideways, and broadsided another car. That was end (for them) of unspupervised test drives in a GT.