trends
We like to think of ourselves as rational decision-makers who are persuaded to accept arguments and ideas on the basis of logical merit. This is laughably divergent from how things really work. The idea itself that humans are rational decision-makers has no basis in empirical observation; it is just some wishful thinking by a small group of philosopher-kings who happened to be very influential, yet it somehow became the cornerstone of western political philosophy for centuries.
Ideas proliferate in much the same way as fashion trends - not because they are closer to some objective truth, but because high-status people adopt them first, and the rest follow the leader. Hair grooming, hat style, gods, and the nature of the cosmos all follow more or less the same pattern of adoption. The rare individual who stands up and shouts, "Wait! But is it true?" is more often burned at the stake than taken seriously.
We do not seek out communities on the basis of alignment of beliefs. We align our beliefs to those of our community. If you spend enough time with people who think blue socks are the only correct kind of socks a person ought to wear, you will eventually begin to wear only blue socks or risk being socially ostracized. If you spend enough time socializing with people who believe that vaccines cause autism, or that rational debate is a tool of oppression, you will eventually either distance yourself from the community, come to adopt their beliefs, or they will distance themselves from you.
This is a rather depressing realization for a person who considers himself to be independent-minded. The truth is that no human being is independent-minded. We are all hard-wired, to a greater or lesser extent, to trust the herd.