To insist one religion is true above all others is to be self deceiving, right?

This is the only option, isn’t it? If you insist one religion is true and all others are false when there is the same complete lack of corroborating evidence for all religions, the only possible explanation is that you are deceiving yourself, right? Therefore, the word of someone who does believe one religion is true above all others, cannot be trusted, right? If they deceive themselves, then deceiving other people would be second nature to them, wouldn’t it?

I would agree in part. It is not that simple. There are many reasons why people think there beliefs about something are true over other beliefs despite lack of evidence or any corroboration.

People start believing something they have huge emotional and other investment in it and despite all evidence to the contrary do not seem be able to look or even research what they do believe or why.