Dictionary definition of Apartheid (as per dictionary.com):
1. (in the Republic of South Africa) a rigid former policy of segregating and economically and politically oppressing the nonwhite population.
2. any system or practice that separates people according to color, ethnicity, caste, etc.
That is a very casual definition of Apartheid. Apartheid in its original form meant "separateness", meaning dividing South Africa into separate nation-states largely based on ethnic lines. The Boers, Zulus, etc. would all have their own countries that they could call home, with sovereignty and international recognition for all. Unfortunately, this idea was quickly perverted by whites who wanted all the land for themselves, while marginalizing blacks to guest worker status, and from there it became the morally indefensible system that came to be known as Apartheid. Even de Klerk, the man who dismantled Apartheid, defends the original idea of sovereign nation-states.
I simply believe that we are too black-and-white when we talk about many political and historical figures. Human beings are complicated, and we should view them as a whole and not allow individual faults to overshadow all of their other characteristics.
None of this has anything to do with what Apartheid actually became and the fact that conservative politicians supported it. But you knew that already.