Free thought is a philosophical position: opinions should be formed on the basis of science, logic and reason, and should not be settled by authority, tradition or dogma. The practice of it is called freethinking, and the people who do it are freethinkers.
It sounds mild until you apply it honestly, because it disqualifies most of the reasons people actually hold their views.
The uncomfortable part
Almost nobody arrives at their beliefs by evidence. They arrive by inheritance, by geography, by who raised them, by which group would be annoyed with them if they thought otherwise. Free thought does not ask you to reject those beliefs. It asks you to check whether you would still hold them if you had encountered them for the first time yesterday.
It applies to your own side
The failure mode of free thought is using it exclusively on opponents. Scepticism aimed only outward is not scepticism, it is loyalty with better vocabulary. The test is whether you subject the claims that flatter you to the same treatment as the claims that irritate you.
Including scepticism of me
The Buddha is said to have told his followers not to believe something merely because he said it, nor because others found his words convincing, nor because it came from teachers or texts or authority. Not to rely on logic alone, or on speculation, or on appearances. To find out for themselves what is true, and then, having found out, to give up what is bad and keep what is good.
That instruction includes the person giving it, which is what makes it serious. Anyone who asks you to think freely and then makes an exception for their own conclusions is asking for something else entirely.
Why it belongs next to rights
A population that cannot think independently cannot notice when its rights are being redefined. Free thought and political freedom are not two separate subjects that happen to appear on the same site. One is the precondition for defending the other.
