I don't think it's the involvement as much as it's duration. Obviously the mission parameters were changed by somebody that protracted the theater of operations for so long.
I think there has been a lack of clarity and consistency around the exit strategy all along.
Clearly, there is a need to change mission parameters based on changing situations, but I agree that the protracted nature of the operation didn't appear to match to a clear mission statement. Soldiers were effectively trying to hold the status quo (more like policemen) but the government spending and strategy didn't appear to match to this.
It was like there was an assumption that putting democratic structures in place, and throwing wads of cash at the military and certain other government institution was going to get the country on a stable footing, if only the military could keep things stable in the meantime. At some point it should have become clear that this simply wasn't an effective strategy, unless you're in there for the next hundred years, to institute generational change. Even then...meh...
That's not a dig at the military, btw. I feel they were given assignments which had no clear success measures. Which has happened to them before, also with poor conclusions.