I'm an atheist myself. I was brought up with a minimal amount of religion at home (it was almost never addressed at all), and actually took some Christian side-education when I was around 14 (I think it's called Confirmation in English too, right?). However, after learning (and thinking) more about religion, I decided that no, I don't believe in this. It's simply asking me to suspend my disbelief too much. Still, I stayed with the church choir as a technician for three years, learning yet more and still realizing that I didn't believe (though it's good to know what I don't believe in, at least). And, let it be said, Christianity has quite a few brilliant points about moral and ethics. It's not that I dismissed everything they stand for once I realized I didn't believe the core story.
One of the things that got me thinking was the religious view on other religions. I mean, if Christianity is true, that would mean Hinduism, Sikhism, Zoroastrianism and all the others are false, right? Logically speaking, and asking a few Christian friends, how could that be? The answers I got were eerily similar to what I had thought myself about Christianity: "They got it wrong somehow", "There's just one religion that everybody worships, a single god to answer all the prayers, but their interpretation is the false one", "Their religion is a construct by man", etc. They could easily see why other religions were false, citing a number of various reasons, but were quite adamant that the same logic could not be applied to their own religion (or the interpretation of the "one religion everybody worships"). It's like they were excempt from the criteria that falsified the other belief systems. When asked why, most said it came down to faith. Now, I don't doubt for a second that the Hindus, the Sikhs or for that matter the ancient Greeks or Vikings had any less faith in their religion that Christians have in theirs, so that argument didn't convince me. If the faith of some people is built on a "lie" and thus can be discarded, how could the faith of other people prove them right? Also considering that everything we know about the universe states it works perfectly without divine intervention, I decided to drop deities altogether and be an atheist.
How did society react? With a shrug, if anything. In Norway, about 70% of the population are members of the (former) state church, due to your automatic inclusion upon birth if both your parents were also members. Still, polls reveal that the number of people defining themself as Christians are below 35%, and falling (the exact question being "Do you believe Jesus was/is the son of God?"). Less than 2% of the population go to church more often than every other month, and even on Christmas Eve, the definite Church Day of them all, attendance is still in the vincinity of 10-15%. Most Norwegians are agnostics or atheists, and being explicitly Christian is, in most of the country, considered a lot weirder than being an atheist. The State Church was decoupled from the State a couple of years ago, now having a name nobody remembers (something to do with Lutheranism or something like that). Even my parents, when I told them, said "Atheist? OK, no big deal" and went on with whatever they were doing. I've got quite a few Christian friends, and quite a few atheist ones too, but in general, religion (or lack thereof) is regarded as "no big deal", something personal you shouldn't flaunt before others.