I post a few things here and there that pique any kind of interest or annoyance in me. I'll post images which make fun of religion or videos which have a good message in arguing against religion. I'm in Ireland and pretty much everyone my age has long ago turned their back on religion. They may not call themselves atheists but in general they wouldn't pay the blindest bit of attention to something criticising religion. It simply doesn't bother the vast majority of my peers.
However, literally five minutes ago I saw a message posted up by a 'friend'. They were a random 'add' from some app or other, so other than knowing them within a game I have no real dealings with them. The message is tame enough "The will of God will never take you where the grace of God will not protect you!" but still makes me wanna ask simply: "How do you know?" There's probably no point asking them this because it won't end well but equally there isn't any reason I shouldn't since the person is neither a friend nor an acquaintance and would have no impact on me if they decide to take offence and unfriend me.
My situation is completely different to yours. Honestly, I'd hate to have grown up in America knowing how religious the people are there and how easily offended they become when the topic of religion comes up. I can't really tell you what to do other than offer the same musings you have yourself. For the friends you value and would prefer not to lose, you could avoid going out of your way to 'offend' them. But conversely, if they are that easily offended and choose to have that impact your friendship, then they probably aren't worth the effort. I know it's more easily said than done but all you can really do is weigh up each situation on it's own merits. If you later find biting your tongue or censoring yourself as a whole is bothering you then maybe reassess how you express yourself and how important those people truly are to you.
European Christianity generally only serves as a 'warm blanket' and not the basis of opinion. The Bible is concidered to be as a piece of philosophical work and (heaviliy modified) historical chronology. If anyone enters a belief or bible passage as an argument or a conclusion they are ostracized from the discussion.
I think this is the major difference between Europe and the US Christians. When I push European Christians belief with evidence, they generally retreat, all the way to accepting science until the big bang. When I push US Christians with evidence they usually end up reciting bible passages and proclaim 'you don't understand because you don't believe'.
My speculation as to why is that Americans are taught confrontational discussion (pro or con) while Europeans are taught consensus discussion (pro and con), making Americans more susceptible to be 'locked in' to an argument and dismiss any counter evidence.
(Please don't take this as an 'all Americans are stupid' type argument, that is not my opinion at all. Not even close, it is a culture and society I hold in deep admiration.)
I find the 'threat of Islam' being quite overstate over here. Most Muslims are not fundamentalists or attempting to brainwash people more than Christians are. We have a fairly extensive history of confrontation with the Muslim world, and it appears to me just to be another chapter. Luckily, atheism and agnostisicm has a very strong foothold in Europe, which is the very reason things tend to quickly become tense when rationality is being drawn into question. We don't like religion or extremism of any sort being superimposed on our societies because we have spent a long time batteling the drawbacks of it.
Atheism has become the norm in most of Europe, and it is spreading at an increasing rate. I don't have to defend being an atheist, a religious person bears the burden of having to justify themselves. Another good thing is that atheism strongly correlated with rationalism, and rational persons are identical across the world since our 'belief system' is the same no matter which culture we were brought up in.
I do worry for America though. You are the brightest light throughout modern history, a society built upon the advancement of the individual by offering the capability of better oneself through education in some of the most esteemed scientific establishments in history. You stand for freedoms only dreamt of for centuries, and used as a template for all western societies. It appears to me you are wasting your place in the world by focusing in bitter internal fighting, essentially taking your eye off the ball. But just as I become disillusioned, you have recently taken the lead in the provision of program and content for mobile devices, a field where Europeans were dominant no longer than 5 years ago.
I hope the US is able to return to its roots as a secular nation sooner rather than later, not just for your own sake, but for the sake of the whole world.
I'm not agressive or really "out" on Facebook yet. I mostly just post sciencey goodness that I feel all of my theist friends just kinda ignore. I do plan on participating in this year's Out Campaign "A" Week, which will be the most upfront I've ever been about my atheism on Facebook. Hopefully it goes well!