That's because that's what they were taught. The same trust in their parents and churches to make them believe in gods are real also makes them believe no one in their right mind could deny gods.

I had a lady, a relative stranger, ask me once, "Why do you hate god?"
I replied, "Why do you hate dragons?"
She, "I don't hate dragons."
Me, "So you believe they're real?"
She, "No, of course not!"
Me, "Exactly, my feelings about your god is the same."
She, "Oh, that's just nonsense!"
Me, "Yes, gods and religion are nonsense."
She stomps off.
Me, walks away smiling.

I've lost count of the number of times that Faithfools have informed me that their Sky Daddy will 'smite' for not believing him, etc, etc.
Shit, he had the absolute PERFECT opportunity about a week ago when I was fixing a couple of loose sheets of roofing during a HUGE Thunder and Lightning Storm, I WAS as wet as a Shag on a riverbank, sitting on a corrugate steel roof, the perfect electrical conductor if ever there was one and I'm still here alive and kicking.
So, from that 'episode' I've come to these conclusions,

1. Sky Daddy DOES NOT exist, something I already knew btw,
2. IF He does exist, He couldn't hit a Bull Elephant in the arse with a Bazooka even at Point Blank Range,
3. like all his Faithfools he too is full f shit.
4. ALL of the above are 110% true.

I've been doing this for so long I've long since realised that at heart many religious people are full of doubt and fear, though in discussion they will double down, triple down, and project their fear onto the non religious. For the non religious, doubt is the oil that greases our minds always to function to look for new information and to question everything. For the religious, doubt is a fearful thing, that must be suppressed. Since the history, the arguments and the logic works against them, their only recourse is to convince themselves that we just don't get it or we are damaged in some way. But look into their eyes confidently that you just know they are on the wrong side of the argument, but they can't let it go.

I simply did some research about my religion in order to convince others that it was true. Instead, I convinced myself that it was not based on reality, but mythology.

A good response might be that atheism and agnosticism are the results of reason, have you ever tried it?

I can honestly say that I've never given much thought to what other people think about my reasons for not believing in their fantasy, simply put.

Actually it is caused by something drastic: learning to think for yourself...

Yep. Same shit gay people have had to deal with for ages. Never mind that nature is chock full of examples of it. Why should they actually even look at nature or evidence in the physical world. Uh, no. Something "...must have happened! ...Satan musta gotta holt un us!"

The most common assumption made by the religious as to you being atheist is that "you must be angry at god." They have this conclusion because their book claims that everybody knows there is a god and that the rocks and trees themselves would cry out the existence of god if they could. This leads into the nonsense of "look at the trees" when others want to convince you of their god.

In the movie God Is Dead we find that the atheist character is angry because god killed his father, or allowed him to die. At the end of this film a priest restores the dying atheist to the fold and solves the whole problem. The success of a second film of this type proves that such movies do make money.

My long time religious friend must feel that I am angry with his god because I did not become the world's greatest evangelist. I tell others that it is because god did not bring me a pony. No, wait! That was Santa Claus.

With me it did...I had time time to read, and think about the bible...found that church services were very much like fox intertainment...

I've heard that before. I think they learn that in Sunday School.

For me it was just a matter of reaching the age of reason and the ability for critical thinking. Hardly traumatic.

Like that guy last week asking us to do a survey that linked poor fathering to atheism. Ridiculous.

My sister-in-law's the sort of person who would ask such a question. I could ask her if she's ever had a bad experience with critical thinking, but well, that would be beyond rhetorical.

Never assume anything. Then you won’t make an ass out of you or me.

                       ASS / U / ME

I left christianity after I read the bible cover to cover. I became a pagan, no punishing god/goddess, no hell. Then one day about 25 years later I became an agnostic. Then 2-3 years later I became an atheist.

I've not had that experience. The people who know me know I'm an atheist, or at least they think of me a very secular, I suppose. I do not try to change the faithful, know a bunch of them, do not wish to get into acrimony; let them do their thing. One, in particular, a former almost Nun, still very religious, commented, once, asking "You don't believe in magic?" and I said "No, I don't." That discussion was not about religion, per se, but had those overtones.
Another one objected to my mention of evolution in a conversation, saying that he could not even countenance a discussion of the topic, as it was against his religion. I felt sorry for him, seeming to be a fellow of decent intelligence, but constrained from even considering such "radical" an idea.
He is a good example of St. Augustine's belief that the masses should remain uneducated.

My drastic was being taught, as a child, not to blindly accept received wisdom. That was from my grandfather, whose own father had been considered a small "r" rabbi, in his own childhood.

I haven’t run in to this. Most theists back away and prefer not to discuss it. I come from a very Catholic family. I have 2 aunts that were nuns and a cousin who was a priest. Only real conversation I ever had with a family member was with one of the nuns. She was in her eighties, we talked for hours. Very compassionate and respectful. We explained how we reached different ends of the spectrum, and were both at peace with the world.

Tougher to believe year after year, built up to critical point so I left. Felt very similar to outgrowing Santa Claus. Wouldn't call that traumatic, more just growing up and maturing.