Freethinker organizations are not religious institutions. They are non religious groups which provide a meeting place to exchange ideas and create "community". Although churches do provide community and a place to meet others they certainly do not have a monopoly on such things.
Atheists who go to Freethinker groups/events do not go there to change their "belief system" which starts the same and is only changed if they decide to become a theist. There is only one belief/disbelief involve and not some system as you erroneously believe.
Freethinking
adj. 1. inclined to forms one's own opinions rather than depend upon authority,
"Free thinker" ; "free thought" are nice sounding phrases that atheist sloganeers have played like a harp ever since the 19th century.
Whether you accept it or not, "free thought" is an absurdity, as thought is not free; it is subject to the law of thought. If 2 x 2 = 4, we are not free to say it equals 5. If right is right and wrong is wrong, one is not free to say that right is wrong or that wrong is right. Your thought is not free. What is free is your will, your power to reckon correctly or incorrectly, to do what you know to be right or wrong.
Now, if by 'free thought" you mean freedom of inquiry, of investigation to learn the truth of the matter studied, then no reasonable person would disagree. But the question of freedom of inquiry is not in the minds of advocates of "free thought". They mean "freedom" to deny God and the moral law as interpreted by true religion. That's what "free thought" has always been about.
"Free thinkers" invariably assume that the intellect of religious persons, especially Catholics, is enslaved because reason and Faith is the starting point of their study and acceptance of belief in the existence of God; where they claim to demand to be shown before believing.
Freethinking
adj. 1. inclined to forms one's own opinions rather than depend upon authority,
When these "free thinkers" send their children to school, they do so with the command that their little ones do what they did, accept upon faith, upon the authority of their teachers, the belief that one plus one equals two, and two plus two equals four, and so forth and so on. By doing so, in later life, they were able to build a lemonade stand, sell x amount of lemonade for 50 cents a cup and determine how much they earned.
Are the minds of those children free? No...they are bound for life to the arithmetic they accepted from their teachers on faith.
But objection is raised from "free thinkers" when the same principle, the same process, is followed in the sphere of true religion.
Children are sent to Catholic schools where they learn to make proper religious and moral as well as material judgments. There they accept upon faith, through the authority of human and Divine teachers, belief in the one Eternal God, Later there comes to them the understanding that by logical reasoning from effect to cause, the mind ultimately comes to the First Cause, God. The religious child grows up believing that God made the world; whereas the "free thinking" child grows up to believe that the world or some primordial mist from which the world evolved came from nobody in the land of nowhere.