You don't have to adopt the ideas of every fringe or contrarian viewpoint you come across to be a freethinker; you simply have to be willing to consider and evaluate those views with the same level of rigor you give to mainstream views. Most people who do that will probably adopt a handful of fringe beliefs but, for the most part, retain a very large number of conventional beliefs too. Julia Galef is kind of an archetypal rationalist/free thinker and she has spoken about the merits of traditional ideas from within a rationalist framework.