The first man who rejected Christianity, and then called himself a "free thinker," built an ideology better than he knew. If a man who rejects Christianity is a free thinker, the implication is that the man who accepts Christianity is a bound thinker--or one whose reason is in chains. It, of course, is not true. But....the "free thinker" is able to freely think what he will even if it is nonrational. He than can label it rational and call it good. "Free thinkers" as a philosophical viewpoint holds that beliefs should be formed on the basis of science, logic, and reason, and should not be influenced by authority, tradition, or any other dogma. It is, however, a dogma eat dogma world and if one presses the ideological notions of a "freethinker" one will find that their foundation is based more in "anti-religionism" as opposed to anything really reasonably "free." And the "anti-religion" sentiment is generally mis-focused. They tend to target anything religious and ask, at the same time, how can all the religions be so divided on issues. It would seem to me that the sensible thing would be to attack the point of contention that bothers their ability to think if they are anywhere near or abouts something that might be remotely religious of nature.
cannot say that I have not heard any preacher say "do not think," but
they have used it in context of a miss-applied definition of faith.
However, if I was to deliver that message and say to a congregation "do
not think," then unless I had a gun pointed to your head at the moment,
you would still have your ability to think.