If you had to sum up the most basic difference between leftists and conservatives, it would be that leftists believe -- or at least want to believe -- that there are no significant differences between human beings. We all have the same intelligence, work ethic, and so on, and any differences in accomplishment are due purely to difference in circumstance.
Conservatives realize that circumstance matters. But they also recognize human beings come in a full range of IQ's, temperaments, work ethics, propensities to violence, and degrees of truthfulness, as well as a whole host of psychological syndromes. And they understand that these variations aren't necessarily spread evenly across race and gender.
The only intrinsic human difference leftists recognize is that there are good leftists, and bad conservatives.
It's all boils down to whether you believe in diversity or not. Leftists don't, even though they have told us ad nauseum that it is the source of our strength.