It is not appropriate to discuss religion or politics during working hours.

All of my acquaintances are religious. My community is small, I can't cut them off because of religion or I'll have no one at all. They are nice but I feel they wouldn't be quite so nice if I spoke my mind.

first, I wouldn't hold my tongue. If they are asking for opinions and it comes to you, then say what you think or just tell them you don't mix politics religion etc at work. If they start harassing you, then report them to whoever will listen. I wouldn't put up with their crap for one minute.

It may be that it is time to find an alternative career path, perhaps by becoming self employed and hence giving no-one any hold over you for your ideas. I know that this may not be as easy as it sounds, but when push came to shove, it would certainly appeal to me.

Thanks everyone for your ideas. We have no HR, and I don't discuss religion at all. The challenge is that when I don't participate in their conversations, it becomes an issue. The best solution has always seemed to be to keep removed from the topic and respectful of their beliefs.

In matters like this I'm cautious to enlighten them to my personal compass for life, also I do my best to separate them in my personal life, when this discussion starts I smile and just listen, or slowly fade from the room.

I live in the UK, but the company I work for is US-based, and many of my US-colleagues are hyper-religious. In order to keep my sanity I make the odd comment when appropriate (e.g. countering a comment that the earth is 4,000 old, when we know that the earth is 4.6 billion years old based on measuring radioactive decay) to simply make them think, and stop talking gibberish and making themselves look stupid. What I don't do is criticise their beliefs, or tell them mine, but it does help me get things off my chest.

pretend to agree with them

I run for political office, if ask about my religion I just state that it is rude to ask such a personal question of someone and the they should be embarrassed for doing so, and they back off or were called on it by someone else as well for here in Canada such a question is still considered to be prying into someones else's personal life by most people.

Outside of politics I don't hide being an atheist at all but, religion seldom comes up in general conversation.

You have to find outlets outside of your career. Work is a big part of our lives and we often use it to establish friendships. You can use meetups for example, to find people who have mutual interests.

If you have an HR department where you work, definitely take it to them.
If no HR, take it to your direct supervisor. No one should be made to feel uncomfortable like that from their colleagues.