I don't think morality and virtue are inventions, although their codification in law and manners is.
I will answer for myself. I am perhaps excessively empathic. I didnt ask to be this way or work toward it; I just happen to be personally distressed by seeing others in pain or discomfort. I am personally made happy by the sight of others being made happy.
When I look around at the world I see people who vary in this tendency. Some I would say are amost pathalogically empathic, and some seem to be entirely lacking in empathy. I assume this is a trait like height or skin color that varies among individuals. To my way of thinking, laws are a kind of prosthetic for people lacking in empathy. They are also a shorthand way of making decisions without having to ponder the consequenses of every little thing we do.