At the base level people are motivated by self interest. Self interest means anything people value, whether explicitly benefiting themselves or helping others. The point is that everyone has a happiness function and any action which increases their happiness is what motivates people.
People develop morals independent of politics. We learn that stealing, lying, and other sins are wrong before we learn the law. In order for arguments to be effective they have have to agree with one's fundamental morality. We need to equate our arguments with what people already believe what is right and our opponent's arguments with what is wrong. This creates a contradiction in people. To rebuke our argument requires abadoning their morality.