Daniel Kelly illuminates why disgust is important:
One way to think of our skin is as a barrier that keeps things out that might damage us. Disgust is a psychological component to this arsenal of protective weaponry. Instead of waiting until something gets into our system that we have to fight to push out, disgust helps us to stay away from objects and people that are likely to get us sick.
Mark Frauenfelder cites Joshua Tybur's evolutionary perspective. Tybur's conclusion:
It’s difficult to think of natural selection actually encouraging the evolution of these kinds of terror-management, anxiety-reducing kind of activities… Whereas traditional models have suggested that disgust serves to protect the self or neutralize reminders of our animal nature, an evolutionary perspective suggests that disgust functions to solve 3 qualitatively different adaptive problems related to pathogen avoidance, mate choice, and social interaction.
The Dish 