I would say there are inherently irrational attributes to racism or sexism. If you can allow for those under what you term
irrational I think I could at least suggest something as to why we're 'crazy' in that sense.
Sunstone said:
Why is that? Why do we have this mix of rationality and irrationality?
Natural selection perhaps, as you seem to suggest with the next question.
Sunstone said:
How did this mix of rationality and irrationality that is human nature evolve?
If rationality can be expressed as ability to seek good information and act on it, it would have obvious (as in I don't need to go into it) survival benefits. In some instances rationality might be a hindrance.
This is just speculative, to give an idea of how irrational behaviour/thinking could benefit us.
In the instances of sex and race (and other ethnic/tribal etc arbitrary lines) rational thinking would, according to my understanding, show us that there is no good reason justifying demonisation, authority, dominance or whatever form the -ism takes. Except, of course, that it might benefit a hypothetical tribesman/woman's genes (and his or her tribe consequently - an extension of his/her gene pool) to develop a fear and hate of 'others' (due to conflicts over resources like land) and would almost certainly benefit genes that happen to find themselves in men to subordinate women. That is to say there may have been selective pressure on humans to be 'crazy' as you put it Phil.
I apologise for my clumsy expression, once I've thought more on the topic I should be able to formulate things more precisely and concisely.
Sunstone said:
What does it mean for the human prospect?
Confused and ignorant people, unable to understand natural biases behaving irrationaly because they believe it's right (or it feels right). It might seem a little controversial to say so, but I wouldn't condemn someone for feeling racist, only acting racist.