I don't think they can be reliably forecasted, and the fact that someone seems to have forecasted it doesn't really show that they can. There are plenty of people in every single administration opposing any given foreign excursion, and it will always be possible to point to them after the fact and make it appear that the situation was a good deal more foreseeable than it actually was. But of course, there are usually perfectly plausible arguments in the other direction, and sometimes those are the ones that win. It is tempting and easy to point to people with the benefit of hindsight, but how do you identify those people to begin with? And if every situation is unique (which is true), how are they supposed to help us the next time?
I doubt that our failures in foreign policy as the result of ignorance. If anything, I'd guess (for neither of us really knows) that the problem of most Presidents is sifting through the mountain of information and variables put in front of them. I don't see any serious evidence to suggest that a mountain of data or a purview of history is going to make decisions any more obvious. If anything, it could produce just as much error or decision-making. This is not to specifically argue for ignorance, but if presented with a situation with so many variables as to render forecasting it basically impossible, at that point I don't see why more data would necessarily lead to better outcomes. And if there's one thing I don't think modern Presidents lack, it's data.
"We just have to try to make better choices" may not be a very satisfying conclusion, but I'm pretty sure it's the correct one.
Your theory seems to be that since nothing can be guaranteed or predicted with one hundred percent accuracy, we might as well not worry about the matter and just intervene as we please while the chips fall where they may. Likewise, you seem to believe that since our leaders and citizens and species prove inherently fallible, we shouldn't be too harsh on them or demand higher standards, or believe that such demands could make a positive difference. I disagree; we need to take a harder look at ourselves and improve, even if we will always fall short of perfection.
And I'm not talking about reams of misleading data, but a better sense of historical understanding and respect for the different histories and prerogatives of other peoples and countries. Clearly, ignorance has existed in these regards or the U.S. Government would not have indulged many of its risky interventions in the first place, at least not in such cavalier fashion.
Nor am I simply speaking to hindsight; as I showed in the case of Vietnam, the warnings existed years in advance. Such was also the situation with Iraq, where George H.W. Bush refused to depose Hussein in 1991 precisely for the reasons that I've cited. However, the next-generation, neo-conservative Bush White House lacked his discretion, his knowledge, or both.
As for "the perfectly plausible arguments in the other direction," they frequently exist (Libya would constitute an example), but they just as often reflect a nearly drunken desire for protecting and perpetuating power, wealth, or unrealistic idealism as opposed to a sounder rationale.