And that results in a bias against existing conspiracy theories, because they generally do not lead towards anything useful. But the bias is not caused by the CT being off mainstream, it is caused by the CTheorists being bad at thinking and clinging to very debunkable ideas (which causes them to be off mainstream in the first place).
I think conspiracy theories are a good thinking tool to some extent which is useful. It conditions to doubt information that may have once been assumed fact, and can teach skepticism which is the basis of scientific thinking imo. Many debunkable ideas are not accepted bc they are just opinion and not based on provable facts.