Respectfully, if you don’t know how long a 2x4 is, I think it would be very reasonable to look this up, as it will make you much better equipped to make this argument.
I generally agree with what you are saying, and frequently haul 2x4s without my truck - but the solution to that is a long flatbed trailer, not a Thule hitch attachment.
it does depend a lot on what you buy it for, but obviously 8' is a good benchmark.
But honestly... at 8' I'm not sure why you're bothering with anything (unless you're getting a lot of them), i usually just threw 8 footers in my Honda Fit and closed the hatch.
Ironically most pickup truck beds are shorter than 8' and most likely a 8' piece of lumber would have to lay diagonally sticking out over one of the edges.
Still good for occasional piece of furniture, lots of lumber, or plywood.
The shortest bed f150 you can buy is 5.5ft, with a 2ft tailgate, trivially hauling 8ft with just a few inches overhang with the tailgate down, and easily doing 10ft lumber.
Again, I think pickup trucks are idiotically oversized and dangerous to pedestrians, but arguing against them by repeating things that anyone that uses a pickup knows is nonsense is not helping win over any detractors.
To be clear, I am not arguing against pickup trucks. The reason I bring up the bed length is a personal pet peeve thing. I have some amount of OCD going on, and I will be damned if I will ever approve of a truck that can't fit a piece of lumber in its bed without leaving the tailgate open that can fit into a Ford Fiesta with the trunk closed.
I am fully aware of why and how people use pickup trucks and I have no beef with that on cultural grounds. But if I were to get one it would be a long bed truck and I would sacrifice the cab space if needed.
I generally agree with what you are saying, and frequently haul 2x4s without my truck - but the solution to that is a long flatbed trailer, not a Thule hitch attachment.