well, to me, the term 'brainwashed' and the phrase 'dogmatic thinking' are closely related and.......
it's not about WHAT one believes, but WHY.
have you looked at alternate opinions honestly and tried to understand them? with religion, for example, most people do not look outside their country or family's main religion. they were just indoctrinated with one religion (Christianity, Islam, Buddhism, Hinduism, etc etc) and never bothered to question.
Same with politics. If you only read sources with like biases (liberal, conservative, socialist, libertarian, etc etc), and then take what these sources say based off "faith" almost, your opinion is not as likely to be well rounded.