A lot of people feel pretty strongly about their political opinions. Often we feel like they are quite set in stone; based on some very deep values that won't change much.
A lot of people also feel like their opinions are based on well-thought-out logic and reasoning, from gathering evidence.
However, there's substantial evidence to suggest that when another tribe's opinions solidify on an issue, our tribe runs away--and we join them. Our opinions on important issues are often fluid and fickle, changing with political wind more than sound thinking.