>”Isn’t it possible that [others] … have opinions and belief systems just as valid as yours?”

There are many people who grant that their religious beliefs may be wrong. It’s worth noting which end of the political spectrum such people are usually found on.

mine is the truth, duh, else I wouldn’t believe it”

I find this to be an extraordinarily irrational position. I believe all sorts of things without believing that they must be right … I believe them because the evidence that I have favors them. But I have believed things in the past that I no longer believe because I learned new things. For instance, I once believed strongly that there was a conspiracy to kill JFK, whereas I now believe strongly that Oswald acted alone. But in both cases I knew I could be wrong. I have many beliefs about history and science that could be overturned by new information … it has happened before. Why in the world would anyone think that something they believe must be true merely because they believe it? That strikes me as absurd, foolish, even deranged.