One of the more surprising findings about political opinions found in Jonathan Haidt's The Righteous Mind:
...political scientist Don Kinder summarizes the findings like this: “In matters of public opinion, citizens seem to be asking themselves not ‘What’s in it for me?’ but rather ‘What’s in it for my group?’ ”36
Haidt, Jonathan (2012-03-13). The Righteous Mind: Why Good People Are Divided by Politics and Religion (p. 86). Random House, Inc.. Kindle Edition.
Perceived self interest seems to be less important than the interest of some group of which one is a member. This finding is a little less startling if you think of political opinions as badges of team membership - public postures, if you will.