why don't schools teach that Abraham Lincoln was a racist?

i just find it interesting that that part of history that we learned so much about every year in school has so many holes and untold stories about.

during a debate in 1858:

“I will say then that I am not, nor ever have been in favor of bringing about in anyway the social and political equality of the white and black races – that I am not nor ever have been in favor of making voters or jurors of negroes, nor of qualifying them to hold office, nor to intermarry with white people; and I will say in addition to this that there is a physical difference between the white and black races which I believe will forever forbid the two races living together on terms of social and political equality. And inasmuch as they cannot so live, while they do remain together there must be the position of superior and inferior, and I as much as any other man am in favor of having the superior position assigned to the white race. I say upon this occasion I do not perceive that because the white man is to have the superior position the n-egro should be denied everything.”

The Civil War wasn't even about slaves. Abraham Lincoln admitted this himself:

"My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that. What I do about slavery, and the colored race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union. I shall do less whenever I shall believe what I am doing hurts the cause, and I shall do more whenever I shall believe doing more will help the cause." The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume V, "Letter to Horace Greeley" (August 22, 1862), p. 388.