It's important to accurately assess the actual level of danger you're facing before you decide to do anything.
Being "right" as far as the law goes but getting hit by a foolish idiot tailgating you still results in YOUR car getting damaged and YOUR life being at risk. Yes, you're within your right to stay right where you are and not get over in the situation you describe... but the safer choice would be to just signal and get over a lane for a second or two and slow down enough to let the tailgating fool pass you so that YOU aren't at risk. Maybe that adds ~20 seconds to your drive - that's a small price to pay for drastically lowering the possibility of having your car wrecked and/or getting injured/killed in a crash.
Dash cam video after the fact may help a prosecutor put the tailgating idiot in jail or get him/her a substantial fine, but it can't heal injuries YOU sustain, it can't bring you back from the dead (worst case) and you're still left with a wrecked car if the fool hits you.
As far as the law goes, in most places you wouldn't be doing anything against the law by not getting over for the tailgating fool in the situation you describe (in fact, the tailgating fool is breaking the law by not leaving sufficient following distance), but in reality laws are only for determining legal responsibility once they're broken and they're only really useful if enforced in the first place. So would you rather put your car and your life in the hands of a law that won't help you until after there's a problem (if it helps you at all), or would you rather just move over a lane and greatly reduce your risk of damage or injury in the first place? I'd just let them pass if I felt they were endangering my safety by driving like an @$$hat and maybe even contact 911 to report their plate and location if you REALLY feel like they're endangering other drivers.