Too many times I am confronted with one-dimensional thinking. And it is easy to understand why. It is simply comforting to stay within the bubble which makes you comfortable, which is en vogue today, which you just need to subscribe to without much resistance. Mainstream means that you can join such mainstream movement without worrying about popular appeal, because you will automatically have that appeal. If your state beliefs easily conform with the spirit of the times, you will not risk anything, but you will also not learn anything, and you will not teach others anything either.
Fringe movements are outside the mainstream and provide a surprising counterpoint to thinking that not everyone will share, alas the fringe. Of course, fringe is risky, and sometimes more than just borderline dangerous. It is transgressive, it is radical, it is inappropriate, improper, sometimes indeed outrightly wrong. But it forces you to learn, as it teaches you an important lesson: Do not just accept things as they are, think the impossible.
Now ideally, both fringe and mainstream are in a equilibrium. Stability and instability, yin and yang, etc. If no idea ever has a time to settle, if nothing is allowed to be stable, instability has no meaning itself. Some ideas move from fringe to mainstream because they deserve to do so, because they prove worthwhile, because they enhance life. Some ideas stay in the mainstream forever, for the same reason. Some ideas remain forever in the fringe because they have proven destructive without ever enhancing life. But that does not mean that the mere thinking about such ideas should be forbidden.
Thinking has to be dialectical. There should not be prohibitions of thought. Such thinking also has to happen within yourself. The old image of an angel talking into one ear and a devil into the other demonstrates this very well: Only if you subject yourself to diametrically opposed ideas, or different aspects of ideas, or even more than just two different possibilities of thinking, only then can real learning occur. When Marx calls for a “ruthless criticism of everything existing” (in Marx to Ruge), this is an excellent suggestion, especially if it is meant to state that everything deserves a critical rethinking, everything deserves critique, and that even critique deserves critique, et cetera.
Action can only be fruitful if all possible avenues, and all possible consequences, are taken into consideration. Too frequently people hide behind good intentions, or claim that the opposing side has bad intentions. But intentions matter only in the confessional. In real life, in real politics, consequences matter, results matter. The assumedly best of intentions can lead to the worst of consequences, and even the assumedly worst of people can do the right kind of thing. Everything else is just fairy-tale thinking.