There are a couple of issues as I see it.
Pulling with an undersized vehicle opens you up to litigation should you be involved in an accident. You might want to talk with your insurance agent.
Pulling at maximum capacity generates more heat. More heat means shortened life span of key components. Transmission, clutch, universal joints, brakes, etc which are stressed. Pull in August and the problem multiplies.
Stopping distances are increased and people just seem to love to pull out in front of someone towing a trailer.
This past weekend while pulling on a forest service road in the mountains of East Tennessee my wife said I smell something burning. We were both wondering if it were coming from our vehicle and then we came up on another vehicle towing a horse trailer in front of us. His brakes were hot and that's what we were smelling.
I know people have to make due with what they can afford, but IMO this is an area where I'd rather have a little to much truck or something that doesn't approach it's maximum towing capacity.
If you're only going to pull on flat ground for a few miles once or twice a year then you might get away with it for awhile.
Personally, I tow with a 99 f350 4x4 dually with a 7.3 liter diesel...rated at 20,000 pounds total gross vehicle weight. It's more truck than necessary but it sure makes towing a whole lot less stressful.
For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places.