Man i make a lot of posts about towing here..
I towed my 09 challenge car (~2500 lbs) on a dolley (~500 lbs) FULL of extra junk (+300 lbs?) behind my dodge dynasty (~3000 lbs) full of 3 people and their luggage (+800 lbs) from TX to FL and back.. over 2k miles round trip. I had NO problems, in fact, it was one of the best, least eventful towing trips ive ever had.
The dynasty gets 23-24mpg empty, and i got 17 with it LOADED down and towing.
I also raced a road raging semi for miles and miles, too.
Now, my dynasty has a trans cooler, a transmission that was put in 3800 lb vans with 250lb ft motors from the factory, a 3.3L motor, the biggest oem brake swap i could put on it, WAY better than stock tires, stiffer suspension blah blah blah. If it was stock it would have been a bad idea because i did feel i was on the limit with that much stuff. I think the GCVW was almost 8000 lbs when the dynasty itself, empty, weighs only 3000.
But like i said, one of the best towing experiences of my life.
Ive also towed with 3k lb jeep cherokees that have more motor and WAY more transmission and found that to be.. NOT good.
I would say it is possible, but the risks people are mentioning are valid. I doubt the car would break.. but if you wipe out or get hit with massive legal annoyances that could be pretty horrible.