Technically, racism is belief of one human '
race' (the term itself being a bit over) being
superior to other. The idea itself is not as
Bad Thing as it is considered today; it is not
beyond reason to theorize that one race, having separate gene pool, could not be somehow superior or inferior to other. Actually, it might even be
foolish to think all would be exactly as 'superior'.
The problem is, 'superior' is hardly a scalar value. Like different species, human races could be specialized to their environments, making others superior in some areas and other races in other areas. Note that I'm not saying "making all to be good at something"; that comment has no base. It is no certainty. It's like saying all computer software is good at something.
But, the logic above doesn't apply in the light of recent studies; it appears that the differences between human races are, except for looks, pretty much negligible. Or so I heard. I think the analogy was, "humans from separate continents have less difference than gorillas from separate parts of woods". The statement above sounds a bit strange, but now that Apartheid has eased up a bit it seems it is correct. Therefore, racism is, now, basically a dead theory.
Fourth, the racism's innocent ideas were, as usual, applied wrong by people who didn't realize, or didn't want to realize, what it was all about. It was only theory, not a justification to kill people before they could prove themselves. That is what made it so wrong that now people are action on racists like racists were acting on other races. Both are theoretically wrong, but since we're not Free World, and people here are inherently irrational, persecuting racists is fine.