With the reality-bending financial incentives that these people have, I simply do not trust your or anyone else's assessment of the genuineness of their beliefs. And anyway, it's quite ironic that from godless San Francisco of all places, we are supposed to simply accept that the harmful acts of religious extremists are justified because, well, they do believe in their cause.
The point here is not the correctness of their beliefs. It's about what the actual content of their beliefs is. If someone says that Donald Trump is a secret Shia supremacist and using that to explain his actions, pointing out that that belief about Trump's belief is wrong is not a statement that Trump's beliefs are correct, but that your model of Trump's belief is incorrect.