Freethinkers often get a bad rap, I believe. Accused of intolerance and arrogance, they tend to catch criticism from all sides. Perhaps rationalist would be a better tag than freethinker.
I included what I thought was a good definition of what a freethinker is. I still think so, although it was concise.
Freethought doesn't mean thinking that is free from the rules of logic. Freethinkers have to go with what is reasonable in light of what we understand about the way the universe works. Here is a link to a good article about scientific testability. It's focus is on Intelligent Design versus Evolution, but it is relevant to matters in general. Let me repeat its key paragraph here for those who don't want to bother with following the link and reading that entire piece:
Whilst a hypothesis is never completely confirmed, if repeated experiments show that a hypothesis is true, it becomes accepted as fact. This process has fulfilled all of the conditions of testability and falsifiability and it is therefore scientific. A theory will always remain falsifiable at some point in the future, however compelling the present evidence.
So there we freethinkers stand. As F. B. Barton, an nineteenth century freethinker, well wrote:
Freethinking implies the being opposed to credulity and superstition—the rejection of what is improbable and unnatural—the disbelief of what is contrary to facts of science, the course of general experience, and the universal and immutable laws of nature, and the incapacity to ascribe to infinite rectitude and goodness conduct in open violation of the principles of justice, love, and mercy.
Wikipedia has a good entry for Freethought found here. I like their definition:
Freethought is a philosophical viewpoint that holds that opinions should be formed on the basis of science, logic, and reason, and should not be influenced by authority, tradition, or any other dogma.
So it is here where the freedom of freethought is expressed: freedom from authority, tradition, and dogma, not freedom from the rules of logic and reason. Open-mindedness has to do with the willingness to honestly examine the evidence, not in the believing that anything is possible.
Then there is the most popular misconception about freethought, dealt with by Susan Jacoby in the introduction of her history of American freethinkers, appropriately titled Freethinkers:
American freethought derived much of its power from an inclusiveness that encompassed many forms of rationalist belief. Often defined as a total absence of faith in God, freethought can better be understood as a phenomenon running the gamut from the truly antireligious - those who regarded all religion as a form of superstition and wished to reduce its influence in every aspect of society - to those who adhered to a private, unconventional faith revering some form of God or Providence but at odds with orthodox religious authority.
So freethought is not atheism using a milder label. It has always been the case that there were more believers in God among the freethinkers than there were outright atheists. Pantheists, Deists, Rational Theists, etc., were always part of the mix.
In truth and in short, what makes a freethinker is the method a person uses in arriving at their worldview.