People believe in many things, often without any substantiation other than that they believe it.
In our 'modern' society it's all to easy to re-enforce low-information beliefs through the "echo chamber" or "confirmation bias" effect(s).
Sometimes, you just have to let go, and let them believe what they are going to believe.
This is true. People that are on the fence when it comes to making a decision need only to hear one thing that will topple then over. My wife for example was listening to CNN on a certain topic and suddenly started ranting. I than told her to watch Fox News and she got to hear a different angle on the same topic, she went back to being on the fence. People will believe what they going to believe .