I guess for me it was when i started studying history and I realized the christians didnt always look like good guys. I was agnostic in like 5th grade and then a depressed but strong atheist by the time i got to high school
What made me become a "Strong Atheist"? - The constant hammering of being told to have respect for those who wouldn't even dream of granting the same to me. My skin has become thinner not thicker over the years and I now lash out at everyone who oversteps that line without exception, friend or foe.
I grew up in a Baptist household, but I was never convinced from the start. My father was a preacher & he use to simulate the act of catching the holy ghost which looked like he had a seizure moment which was bullshit. My mother raised me as a single parent & she was never was big on religion. She use to tell me to choose if I wanted to believe in a god or gods or not. My grandmother forced me as a child to be baptized & once she realized that I never went to church or paid my church dues I ask her to stop paying them for me to discontinue being associated with her church. What makes me a strong atheist in which I also trust that all atheist are strong atheist is the fact that I have been & will always be an empirical individual who uses deductive reasoning & the scientific method to explain any and everything that I had questions about. I personally feel religion should only be referenced as the history of explaining how primitive men & women thought processes were during the bronze age of man used to explain phenomenon that they could not explain until the tool of science freed us with the power of knowledge using empirical evidence. If it was up to me if humans did not use the practice of using the scientific method & common sense in their daily lives. There should be penalties & punishment for using any religion to live by before the facts of empirical evidence.
Religions make hating a virtue. The evil people are clearly defined, god hates them and so should you. Doing what I can to help to eliminate the needless hatred and the needless suffering engendered by religious myths is my gift to the future. Just like the people in the past payed it forward so I can have what I have today I will do the same for my descendents. We seem to have gained a large amount of ground in a short amount of time.