the more someone plasters his vehicle with bumper stickers and decals the more territorial he feels about the space inside

Sorry but to me that reads like made-up left-wing nonsense. "Territorial" about the space inside their car?

Nobody ever thinks in these terms. Unless someone is actively trying to carjack you, the space inside your car is never challenged, at risk, or up for grabs. It never even crosses your mind. You just get in your car and go and never think about the "territory" therein.

It could just be more likely that the bumper stickers mean the person has a lot to say and likes to say it in this manner where just driving around gets their message out to hundreds of people at a time. Crazy, I know, but it could be.