I'm a non-religious person from Sweden and have a hard time understanding why it's such a stigma being an atheist in America?

From what I understand there are people hiding they are atheists. From an outsiders point of view, I find the religious side very hostile.

Atheists are sadly the least trusted form of person in U.S. It's rather sad not being able to state you're atheist because there have been incidents in different states. It's a big deal in U.S because mostly Christianity wants to take over and throw its law around. Mostly because atheists don't believe in god, people who are religious feel threatened that their faith is in danger of being taken simply because we choose not to believe in god.