What's insane is that they now reject ALL possibility. It's not that they believe there is a very small chance that something could happen and they decide to take a risk of less than a fraction of a percent, but they straight up believe it's impossible for things to happen, even if common sense points to it as well. You don't need to be a scientist to know that changing your body's functions to synthesize proteins that you believe are what causes harm to a person will harm you and can go past what you intended it to do. They even reject their own beliefs to reach the same conclusion being fed to them.