Because I sure do!
Actually, I had been skeptical about religion since the 6th grade, but I had not considered atheism until about four years later. The moment in which I declared myself an atheist, to no one's surprise, happened in my 10th grade theology class. We were having a lesson on the ten commandments, and my teacher said that god would always forgive you, no matter what commandment you broke as long as you are truly sorry, but the only unforgivable sin is the complete rejection of his existence. So, according to this woman atheists are worse than murderers. That was the moment in which I decided that I was an atheist, and I have never looked back!
This reason is not the only reason, but it would take a book the size of a set of encyclopedias to list all of the fallacies of the catholic church, so even if you do not have one exact moment that led to your deconversion, list some of your reasons. I am sure that we will all agree with you!