Our lives are full of important and interesting questions.
One is 'How should I make decisions about ideas?'.
Good ideas have explanatory power, and can change our ways of thinking. They prompt us to make small experiments to determine whether we can improve our ways of doing things.
Good ideas may be wrong. Good ideas that are wrong are easy to discard. Bad ideas are hard to discard even if they are wrong.
Bad ideas usually have some social element to them, which reinforces the difficulty in discarding the idea. I will use denial of climate change (AGW) as an example:
Is the world getting warmer as a result of man-made emissions? Some people don't believe that it is.
This was once a good idea, even though it was always wrong.
What is a really BAD idea is the idea that there is a conspiracy to promote AGW. This is a belief with a social element, that makes it difficult to discard.
Denialists cannot discard a potentially good idea (no AGW) when overwhelming evidence to the contrary is presented, because the social content they have added to their belief (conspiracy) makes it difficult for them to do so.
So, what is a free-thinker?
A free-thinker is a person who rejects bad ideas that will hinder them in the search for good ones.
Let us take the example of religion, which can be restrictive to free thought.
Firstly, religious ideas are not good ideas, as they do not have explanatory power.
Theists explain all events with a single explanation: God's will.
This single explanation is supposed to cover every instance of any kind. It has no explanatory value. God wants everything that does happen to happen. Does that sound circular to you?
Secondly, religious ideas are bad ideas. There are social elements included in religious ideas that make them very difficult to discard.
The major monotheistic religions all hold that non-believers will be punished for eternity after they die. This idea has social elements (consequences to the individual due to their belief or non-belief) that make it difficult to discard.