To a certain extent, the increasing sway of Arabs over our educational system reflects the lamentable influence of petrodollars in our economy. Textbooks are moneymakers and so are legitimate economic targets, but that doesn't explain the subversion of our history and social studies curricula. Publishers can make as much money publishing truthful accounts of Western civilization as they can by publishing pseudo-historical narratives. To understand the pro-Islamic perversions in our school textbooks, we must understand taqiyya.
I would go one step further and argue that we need to understand the subtle tactical difference between taqiyya (the dissimulation and concealment of one's convictions) and kitman (the dissimulation and concealment of one's malevolent intentions). See Daniel Pipes piece on this topic.
As with many such cultural challenges, this is a bipartite assault. Externally, the highly motivated political Islamists (whether they be Wahhabi, Salafist, Ikhwan, or some other militant manifestation) wish to elevate Islam in the West and weaken the ability of the West's defenders to counter or resist their messaging. That is, taqiyya paves the way for Sharia. In order to accomplish this goal, they must sanitize their history and sugar-coat their doctrine.
Internally, the radical Progressive left (the inheritors of Gramsci's "long march through the institutions") have been working steadily and tirelessly for decades now undermining the cultural confidence of Western societies. In many ways, they have behaved as a fifth column. Whether it be the imposition of social policies/ideologies such as official multiculturalism (the formalization of cultural relativism), or the pedagogical drift toward victimology in the classroom, their messaging is the same. Western culture (indeed western civilization in toto) has everything to apologize for and nothing to celebrate. Any expressions of cultural or civilizational confidence, in fact, will be put down sternly with a reflexive and feckless charge of "racism". You could set your watch by it.
Yet, in spite of the obvious absurdity, the tendency of some progressives to equate opposition to -- or criticism of -- an ideology with the hatred of a person on the sole (and indefensible) basis of skin colour or ethnic background has already become regrettably commonplace. So successfully has "the long march through the institutions" progressed.