A few people have posted that they have run with passenger tires on their trailers for years and never had a problem. All I can say is that it's not recommended because of their construction. Sidewalls on a passenger tire are thinner for a better ride and the tread design is for traction. Trailer tires have thicker sidewalls for better control and a tread design for less resistance to rolling instead of traction.
My AS follows my TV very well, never had an instance of sway, with cross winds or trucks passing me, even one after the other. On our way home from Texas last month I had signaled to change to the right lane, started my move and a car that was behind me gunned it and began passing on the right. Just reacting to his maneuver I pulled hard to the left to stop the lane change and that's the first time I felt anything close to sway. It came back right away, no problem but I am glad to have the ST tires.
If you've been running passenger tires on an AS maybe you've been lucky and never encountered an emergency situation. There are lots of risk takers in the world, I'm not one of them. I don't see the point in using a tire that is not designed for a vehicle application, particularly if the tire industry says it's not safe.
My family is too precious to me and there is enough risk just being on the road. I'm playing it safe. Your mileage may vary.
Rich & Yvonne
2006 Safari SE -Dora-
2004 4Runner SE