Part of the reason for what you are describing has to do with the fact that we live a world where being incorrect about something is equated with being or doing something wrong.
Being incorrect or mistaken is not exactly the same thing as doing something wrong or being bad. But from childhood onward we are raised in a system where being correct is rewarded, but being mistaken or "getting it wrong" is frowned upon, even punished.
I can remember being spanked badly for bringing home a failing grade. I look back at that and think: How ridiculous! I failed in the class not because I was a bad child or misbehaving. I actually failed because I didn't comprehend the material. I used to have a learning disorder when it came to numbers, much like dyslexia with reading. But back then they didn't know about this (most don't know about it today either). So teachers told my folks I was not paying attention in class or caring to do my work. It wasn't that. I really couldn't do it.
Once my situation had been properly diagnosed and treated I could perform well on any math exam, especially in advanced forms of mathematics. But the experience left a scar that told me deep inside that if I ever made another bad grade, I was being a bad child, a bad human being. This stressed me out for the rest of my school days.
So when it comes to ideologies or convictions, whether they be religious or not, we are in effect still acting like children. We want to be right because we believe that being mistaken is morally wrong in one way or another.
We even "punish" those people we think have a mistaken view. We tease them, call them names, treat them badly. But for all we know this person may make claim to a conviction simply due to a mistake they made in judgment. They don't correct themselves because they, like you, think that if they are wrong about what they believe that this makes them in some way bad. No one goes around thinking they are bad or mistaken. We all believe or want to believe we are right, good, and enlightened.
We argue because we are in some ways still defending the child in us that see challenges to our personal convictions as inciting us to be "bad children." We are not bad, we tell ourselves. We are good! So we resist because we want to keep acting like a good child, sometimes at the expense of opening our minds to evidence, reason, and logic. We want to fight, prove the other wrong, shame them, silence them, even destroy them because their existence challenges our inner child's desire to feel that we are not bad.
It is wrong the way people treat others on this forum and in real life when you consider that people quickly ridicule the beliefs of someone who doesn't share their own. It's illogical because we don't know why the other person holds on to their convictions or exactly how the person understands the convictions. These types of behaviors are mere reactions, not thought-out responses.