But now we're getting into "blaming the victim" territory with all the confusions inherent to politics. It makes me wonder if a strong desire to be sympathetic, translated into controversial political questions like these, limits a person's likely appreciation for cultivated rationality?

A little knowledge is a dangerous thing. Assume for a second the hypothesis is true: Slaves became slaves because Africa wasn't rational enough. If we are sympathetic based on false beliefs, then we will not be able to offer them a true solution. We might offer them our sympathies, or be more willing to donate to their cause (even if it's irrational), but we won't be able to stop it from happening again.

If we believe that people could have avoided these tragedies through rationality (assuming this is true), then we automatically have the solution for avoiding these tragedies in the future. Just add rationality! It doesn't matter how sympathetic we are if all we do with our sympathy is wander around, looking for the answer we've blinded ourselves to.

Sympathy is more than just feeling bad for the victim while you let them get exploited again and again. Sympathy is understanding the victim and having a desire to help. Clear, truthful understanding of all causes of victimization is a prerequisite for both of these to occur. You cannot understand a victim until you understand how they truly came to be a victim. You cannot provide meaningful help until you understand their role in the problem. Sympathy without rationality is just worthless pity.