If they are not detectably different from good drivers, doesn’t that make them good drivers?

The aggressive drivers I personally know are always aggressive.

I think there's more variables to it than that. It's absolutely possible to create aggressive drivers out of thin air if you annoy everyone around you enough. I used to drive commercial equipment that simply couldn't keep up with normal traffic. Needless to say when you are a rolling obstruction you see a ton of "aggressive" drivers because "normal" drivers do aggressive stuff rather than get stuck behind you. I can't imagine how bad it would be if I were driving like that in a vehicle that didn't very visibly have an excuse to be acting that way.