You have very valid points and an excellent argument, but you are forgetting a single thing: People suck.
It's true. A single person can be intelligent but when you challenge the things they believe in adamantly their IQs plummet and they revert to the jabbering animal we all know man is under his civility.
It's something we all have known for all our lives; people suck. I suck, you suck, the world sucks, we all suck and are no different from one another. You can try to educate people and you may reach a few but the ones you don't reach will retreat further into their own worlds where they and the folk who think like them are the only ones who are right.
We've all, at one point of another raised our voice during an argument or debate or lashed out at someone because they challenged our beliefs.
The movie "Dogma" said it best: "I think it's better just to have ideas, you can change an idea. Changing a belief is trickier, people are willing to to kill for it, willing to die for it."
It's not just theological beliefs, it's your belief in anything, people, politics, life in general. If you challenge what someone believes in and keep challenging it they will defend it, violently if they have to. And even knowing this won't stop you from acting this way; it's human nature...
Or I believe it to be anyway.