Neo-Neocon explores "The unintended consequences of teaching expurgated history":

In my day, what was left out was anything that was too complex, and also anything that conflicted with the perception of America as a righteous and near-perfect place—which included any personal foibles and imperfections of the Founding Fathers (and of course, anything remotely related to sex). What’s left out today is anything that isn’t politically correct on either side (which of course is virtually everything of truth) and anything that might make the US look good (I’m engaging in only a slight bit of hyperbole there, I’m afraid).

In short, anything of interest is left out, as well as anything that would meaningfully connect the teaching of history with the problems we are facing today—which would be what would make it most interesting and most helpful.

The consequences of putting history into a blender and turning it into bland, featureless, and easily digestible pap is not just having students who are bored to tears, although that would be bad enough. Nor is it just that history textbooks now have a strong bias on the Left, although that isn’t a good thing either. The worst effect is that such an approach to the teaching of history creates an ignorant and naive populace that is even more condemned than would otherwise be the case to repeat history’s errors.

I’m convinced, for example, that failure to properly teach the history of the wars that we have fought in the past—their complications, controversies, and errors, as well as what led to them and what was accomplished by them—has led to unrealistic and simplistic expectations of warfare itself.

And, come to think of it, perhaps this is not an unintended consequence; it’s possible that the current overarching Leftist bias of the writers of today’s textbooks include a pacifist agenda, of which this is part.