So basically going back to domer's original two concerns, we've really got them boiled down to one. It IS feasible for the U.S. Army to pull out with minimal casualties. And I like the unspoken implications of Mr. Perceptive's remarks about equipment left behind: "Shoot at any of our departing helicopters and all this fine equipment we are leaving behind will be fucked up so badly you won't even be able to use it for boat anchors."
I deal with domer's second concern as follows: It's speculative. You can't base your decisions on a bunch of maybes and what-ifs. The British pulled out of Palestine in 1948 and all hell broke loose. It wasn't exactly unforeseen and the repercussions are still being felt today, but still from the British POV, the decision to pull out when they did was the right one. Deal with today's problems today, domer.
Tomorrow will take care of itself. Always has, always will. Fear of tomorrow should not be the excuse that paralyzes you today.
"So, first of all, let me assert my firm belief that the only thing we have to fear is fear itself - - nameless, unreasoning, unjustified terror which paralyzes needed efforts to convert retreat into advance." - F.D.R., First Inaugural Address