I say this a lot, but all humans are heavily biased towards believing their in-group. For some people that's basically all that matters. I feel like authoritarians, right wing authoritarians, are especially prone to this. Facts and figures don't matter. It's the emotional core of "fit in with the group" and "outsiders BAD" that's driving it, and all the justifications come afterwards.
I don't want to say anything like they're like animals or subhuman, because this behavior is extremely human. We all do it to some extent. It's just for some people it's so dominant, and their in-group is so dangerously stupid, it's a real problem for all of us.
Some people are more or less followers, but we all have it to some degree. You're more likely to believe a trusted source than someone you've never met before. If your best bud tells you a game is good, you likely give it more credit than some random guy on the street, or a guy wearing the t-shirt for a sports team you hate.
edit: I forgot i usually link this comic https://theoatmeal.com/comics/believe
it's a very similar idea