When I type 'religion' into the kindle book store, I see mostly Christian books. In America, we have convinced ourselves that Christianity IS religion. Most people can only associate the word God with Jehovah, despite its potential to mean the Muslim God, the Jewish God, a Deist God, or ANY other God. It's more than the word God. We barely bother to differentiate people who call themselves religious and people who are devout Christians. I am a very religious person. Tell that to an American, and they will assume I am a bible-thumping Christian.
Atheists do this too. Especially with the term God, but also with religion in general. They savagely attack Christianity, but claim to be attacking religion in general. They disprove Jehovah and then claim to disprove God. They are ultimately unable to get rid of the idea that Religion=Christianity. Not just Atheists, but most Americans. Perhaps there will be some minor nod towards Islam or Judaism, but ultimately when most people say Religion, they mean Christianity.
Not only is the idea obviously stupid, it is hurtful to EVERY OTHER RELIGION that isn't Christianity. I want to be able to go outside, have a chat with some random stranger, mention that I'm religious, and not talk about Christianity. We must do our best to fight this notion. Every time you see an atheist attack Christianity, but claim to "disprove religion," correct them. Every time a Christian claims that the religious are being persecuted, correct them (both on the fact that Christians are being 'persecuted' and that they are almost certainly not being persecuted). Nothing in today's America can be more harmful to the idea of religious freedom than assuming that religion is Christianity.