If you rear end someone, you are at fault regardless. I don't know how someone in front of you is supposed to "give you room". It is the driver's responsibility to maintain and control their vehicle and not cause accidents.
Commercial drivers are weighed and required to comply with GVWR (mostly for tax reasons), but for non-commercial vehicle drivers in the US, the door sticker is a manufacturer warranty and liability CYA. They are the ones who determine what that is, based on any criteria they wish, and it is only valid for the stock configuration. No one is going to weigh you and you won't get a ticket. I'd bet a majority of 1/2 ton pickups with campers out with the family for a weekend are over GVWR. You may get a ticket for an unsafe load, but that is a visual determination and judgement call by the cop.
Of course you can improve the ability of your truck to handle well while hauling weight, with tire and suspension upgrades. Other parts may wear out sooner but that is not a safety problem. A case in point is the Truckhouse camper, which uses a modified Tacoma chassis, and is way over GVWR empty. They've modified the rear axle and frame as well to address durability concerns, but the sticker can't be changed.
