Mostly by the fact that the various camps in this conflict do not fit neatly into the simple dichotomy that we in the West -myself included, much of the time- find it all too easy to draw. There is a spectrum, and the various groups fall into various points among it.
I agree with you that people should never be barred from education on account of gender, but note that I used the word never: a word I think you would also be willing to use. That's an extreme term, in the sense that there's no way to go further, and that puts us solidly on an endpoint of the spectrum. This isn't a bad thing, but we need to acknowledge where we are, because it means that we have a question of idealism versus pragmatism to consider.
In a place like Afghanistan, support for our side therefore depends in large part on which groups we are willing to accommodate and which we are not. If we accommodate only those which agree with us in total, we will never get anything done. The pragmatic way takes longer, but it is less likely to be pulled out from under us in one stroke by the likes of the Taliban. If this is worth doing -and I think it is- then it's worth doing in a way that will stand up to the next hundred years of conflict.