I may be making a generalisation, but most of we atheists of advancing age started off as having some sort of affiliation, or were indoctrinated into, a mainstream religion. I was adopted by C of E parents who had to go to church to be approved to be able to adopt me, was baptised, went to a C of E school, was confirmed, and eventually made the decision that things didn't seem to add up, so I did some reading, looked into other religions (especially Islam and Bhuddism), visited a mosque and a Bhuddist centre and asked some questions, along came Carl Sagan's Cosmos TV series, and I came to the conclusion that there was no god. In 1999 at the age of 42 I found myself in cardiac intensive care with congestive heart failure which came to light when I presented at A&E having had a stroke. The cardiologist said we'd know more within 2 weeks, assuming I survived that long. I well remember laying in bed thinking if there was ever a good time to do a deal with a higher power this was it, but try as I may, and even with all the indoctrination into Christianity I'd had, I realised there was no logical case for belief and went on to the revelations that if I died (1) I wouldn't have to do my tax and (2) I'd never find out how Star Wars ended. Hence this is me - I'm an atheist.
Let's put aside the statistically insignificant minority of people of faith who follow religions such as Islam, Hinduism, Bhuddism, etc. in Australia, and the larger group (but still a statistical minority) of C of E, RC, Uniting Church, Mormon, Jehovah's Witnesses etc. within the Australian population who it would be reasonable to say were brought up in their religion and continued, or perhaps lapsed but then returned to the flock.
In Australia at least, over the past 20 or 30 years what is popularly portrayed as Christianity seems to have become the domain of the evangelical movement, especially pentecostals and baptists. The Assemblies of God Church here even has a political arm called Family First. Let's just say that a typical cross-section of their followers is not particularly well educated so not really capable of following logic or framing a good argument, and is looking for easy answers readily provided by the polished and smug real estate agent / Amway rep style of often unordained pastors, who will not hesitate to paint any other religion or subset of their brand of Christianity as misguided, a distortion of "the truth", or even the work of the devil. With their redneck American style of evangelism Islam becomes an easy target. They do put on a good morning tea and their music, while usually plagiarised pop songs where God or Jesus has been subsituted for darling or sweetheart, is at least catchy and gets the toes tapping and the hands clapping. When they're not having one on one conversations with God they're busy pasting urban legends and ill founded right wing political mistruths into their statuses on Facebook.
I'm happy to discuss religion with the first group, but I'm buggered if I'll waste my time on the second. As Billy Connolly would say - They're more to be pitied than scorned.