"How can you be so certain you are right?"
Let us begin by distinguishing between political liberalism and metaphysical liberalism. Political liberalism is focused on the activities and institutions of governance. Its rough outlines include insistence on certain basic rights, such as free speech, some level of respect for private property, the right to free assembly, etc.; and a preference for a certain type of governmental institutions: democratic, republican, non-hereditary, accountable, and so on. Many, many people are political liberals who are not what I would call "metaphysical liberals": these political liberals' own metaphysical beliefs may be traditionally Christian or Jewish or Muslim, for instance, but they believe that the best form of state is neutral between such commitments, and is broadly liberal in character. While they might strongly believe that, for instance, pre-marital sex is wrong (and not just "wrong for me"), they don't feel it is the place of the state to correct such mis...