Would probably flow more naturally and avoid unwanted conversation if you used "on earth" or something else universally experienced instead of "in athieism" which leads to the same problem you were complaining about but from a different group.
Sorry if I'm being unintentionally obtuse, this is a genuine question, what's not normalized about it? I can't remember the last time I had a conversation about my faith or lack thereof. Could just be my location and circles I hang out with, but I don't know many people, especially my age or younger, who really care one way or another.
There's so much more to it, but the short version is that a huge portion of this country doesn't consider atheists trustworthy or even properly "American". God is on our money, the bible is used for official government ceremony, most of our public holidays are Christian, the word holiday and tons of others are explicitly rooted in religious culture. In-n-Out has a little bible passage on their cups.
Being openly atheist is a radical position in this country, one that will limit you professionally and socially.