I have never encountered any hostility as an atheist when I have been in the US before. I have to agree with @Tellenbach, I think that there are a subset of atheists who are very zealous and stir up a lot of conflict in the community they live in, though maybe it has been easier for me because I am politically conservative.
Superficially I wouldn't object to secular activism as I share many of the activists' concerns (such as separation of church and state), but often these people are the ones who focus on really pathetic things like disrupting Christmas decorations, turn around and apologise for fundamentalist Islam, Judaism, Hinduism etc, and support open borders which allows more religious zealots to enter the country. I therefore see them as politically motivated Leftists, rather than genuine atheists who view religion as a negative force generally.
The reality is that outside Africa, very few Christians go on killing sprees anymore. Can you say the same for Islam? Abortion/contraception is also much more of an critical issue in third world countries than in the U.S, which actually has a fertility rate (1.9) below the replacement threshold. How many of you knew that?