In Richard Powers' novel The Echo Maker, the protagonist's brother suffers from Capgras syndrome, a fairly rare disorder in which the patient believes that a loved one or loved ones have been replaced by perfect replicas. One theory about Capgras is that the sufferer has a disconnect between the part of the brain that recognizes the loved one and the part of the brain that has an emotional connection with that loved one. They look right. But they don't feel right. Given the choice between an objective truth and an emotional one, the brain chooses to rationalize the emotional one. The person who looks like my sister must be an impostor because she doesn't feel like my sister. None of this is conscious, of course. The patient just knows they're right.
Choosing to base our objective judgments on emotional "facts" is not, however, pathological. The entire marketing industry is based on the (usually correct) notion that we decide what to buy based on emotional processes, not rational ones. Ditto whom we vote for. As a species, we tend to pick, then rationalize, not the other way around. Traditionally, though, we've always believed that emotion resides anywhere but the brain. "Follow your heart," as they say. What science seems to be telling us is that the "heart" is in the brain, and the brain is very good at passing it off as "reason."