I pull them back out because it is not inhumane and it gets the job done. They are not traumatized but just go on like that is how they have done it all of their lives.
They are creatures of habit that can talk themselves into being afraid of anything you have allowed them to and then reinforce.
I just create a new habit and 'norm' for them. From that day forward, THAT is the way they get out of trailers. I have never seen any value of taking forever to do something that is done just as easily in one day.
And, I have seen many horses that people have tried that method with and once all four feet were in the trailer, the horse still refused to step down -- all that after spending days to get the horse to step back out of a trailer one, two and three feet at a time. Then, they still brought the horse to me to teach to get out backwards.