The reason we so genetically programmed is so that we naturally project our weak and helpless newborn children without having to be taught to do so. If this was not the case humans would have died out long ago. Sorry, but as much as we love cats the vast majority of humans are going to have a weakness for the more helpless rodent. I think this support of underdogs has anything to do with children. Cats take good care of their offspring but that doesn't make them start feeling compassionate towards potential enemies.
Ignorance can be dangerous.
Think about that next time you bite into a hamburger.