Seeing as Sweden is a prominent example in this debate (and no wonder, I believe we have the largest Atheist/Agnostic percentage in the world), I'd like to add my two cents.
Religion here is not a normal part of intergrated society. Since before 2000, all swedes were born into the Swedish State Church (Evangelic-Lutheran) but the church attending percentages are below double digits. I believe the cause for the large atheism pool in Sweden may lie in these points:
- We have mandatatory classes named simply "Religion" (same word in swedish too) were we are taught the different religions without emphasis on a single one, we learn to compare them (what similar origins do the main religions have?) and to overall, see things for several different perspectives (the swedish neutrality thing).
- We have not been in war for around 150 years. No war = not many dead = no need to pray for souls, find comfort in religion, needing to strenghten the internal patriotism (God bless america?).
- A very liberal state church. The swedish church has always been very liberal and open (A very, very good thing in my opinion) but this also means that religion is not tied to the state (even though formally so on paper) and not fundamentally and part of society. Unlike for example states like Pakistan, which are BASED on a religion, (even USA, although freedom of religion is in the bill o rights, is founded on, with and continuing to strive for, mainly christian ideals)...
- Modern, industrialist country with a very international point of view. More cultures/religions = less likely to pick one (not always true, but still.)
Anyway, I think that religion will always be around. And personally, I don't object to that. I only object to religons that in any way hinder people from finding happiness. (Aka, muslims killing homosexuals, christians shoving their religion down peoples throats, hindu condemning people to a horrible life...)
I also believe agnosticism (I count myself to belong to that group, or atheism... Have not made up my mind. But they are actually vastly different) will be one of the most prominent religious groups in the future.