And they really don't like it when you point it out to them.
Just so. As St. Paul says, “The law of God is written in the heart,” so that even the Gentiles have a conscience that tells them what is right and what is wrong.
And if you ignore your conscience, it can become like a “burning coal.”
Those who ignore religion and traditional morality may not know why they feel uneasy and guilty, but a statement like Santorum’s can hit them unexpectedly hard. So, they shout back, hoping that it will go away.