Asking for evidence is a fair point. Personally, I'm not going to risk my freedom and my future financial security on the good graces of a DOT officer or a personal injury lawyer. "Yes, I was overweight, but I promise that's not why the accident occurred!"
I took a firearm safety case from Massad Ayoob some years ago. He is a law enforcement officer, professional firearms instructor, and professional expert witness in firearms cases, so this isn't just a case of "some guy" saying it. He talked at length about how when you are in front of a jury, it is critical to minimize the number of ways that the prosecution (or the plaintiff, in a civil case) can pick you apart and make you look bad. If you modified the trigger on your gun, that can be used to discredit you, even if in reality the modification was irrelevant. I think of that general approach when I think about whether I want to tow overweight or not. You, me, and the gatepost may be certain that my truck is safer with a gooseneck than with a bumper pull, and we may be right, but if worst comes to worst, some lawyer is going to point to the manufacturer's spec sheet for the truck and ask whether I was over it. And if that day comes, I want to be able to say, "No, I was not."
The difference between guns and trailers, to me, is that I am pretty much in control of who I shoot, and I am very unlikely to ever shoot anybody. But I am NOT in control of who I get into an accident with on the road, and I am very likely to get into an accident or two in the years I have left.
The McDonald's case is commonly held up as an example of an un-deserving plaintiff winning an un-just award from an incompetent jury. The facts about the case are actually not well known, and support the plaintiff in many ways. You can read up here if you like:
https://www.ttla.com/index.cfm?pg=McDonaldsCoffeeCaseFacts
