I'm confused what you're trying to say here, are you trying to say that more damage will be caused, or that there will be some different amount of liability if somebody runs in the back of your vehicle and you have a hitch in versus a hitch out?
Generally speaking (from what I understand) if somebody rear ends your vehicle they are considered to be at fault because they were following too closely, whether or not you have a trailer hitch installed in the back of your vehicle would not be considered to be relevant.
If they hit you hard enough to damage something on the trailer hitch sticking out, they would have hit you either way, it's just a question of whether they need a new radiator as well, or just a front bumper.
Aaron Z