Can Decline in religious belief improve society?
Secular nations like Sweden and Denmark are happier than the United States which is overall more religious. Further the United States Bible Belt suffers from many social problems that are less severe in more liberal and more secular parts of the United States. So the answer could be yes. 
Getting scientific proof in the social sciences is generally much harder than it is in the physical sciences so more careful analysis is needed before we can say anything definitive. Preliminary research suggests that religion may actually be bad for society.  One individual study isn't conclusive but when a wide range of publications all come up with the same result, that religious do worse than more secular orientated societies that becomes significant. What hasn't been shown is whether more liberal belief systems, notably Liberal Christianity are also harmful. Altheratively these less extreme religious types may not be doing enough to compensate for the harm that Fundamentalist Christians and Fundamentalistsfrom other Faiths do.
United States of America
For one thing social problems in the US Bible Belt date back to the Civil War in the 19th Century and to the times of slavery before that. Sorting out how far the poisonous Christian fundamentalism is a cause of social problems and how far social problems cause Christian fundamentalism would require extensive research. If any American graduates reading this are considering doing a PhD you could discuss this project with your supervisor. Intuitively the following looks likely.
- Social problems exacerbate Christian fundamentalism in the US Bible Belt.
- Christian fundamentalism exacerbates social problems in the US Bible Belt.
- Secular Americans: Freethinkers in a Free Market of Religion
- Atheism on the upswing in America
- Is religion good for society? And the USA won't do worse if religion declines.
France and the USA compared
In France there is a principle of laïcité which is hard to define but seems to mean that the state is separate from religion. Theoretically this applies in the USA as well but religion was taught there till the Madalyn Murray O'Hair brought a defining court case. Intelligent Design is taught in many US states and there are continual complaints about unconstitutional religious activity in US public schools. By contrast in France laïcité is respected and French public schools (state schools in UK English) teach school students to evaluate other cultural belief systems as well as their own. 
Footnotes and references
- This article is about secularism rather than atheism because in practice agnostics freethinkers generally, even deists are likely to frame government in secular terms and follow political ideologies that are similar to what atheists choose.
- Cross-National Correlations of Quantifiable Societal Health with Popular Religiosity and Secularism in the Prosperous Democracies This long document doesn't prove conclusively that religion worsens society but suggests religion might be harmful.
- What is French "Laïcité" (laicity)?
- Can secularism improve society? Link which will work
- Can secularism improve society? Permanent link to the article as it was at 6.30 pm UK time 29th Aug 2012
The links below deal with Scandinavia, I plan to write about that later’’
- Secularism:The Case in Denmark
- Society without God
- Scandinavian Nonbelievers, Which Is Not to Say Atheists
We hope you like the external links we've found for you though we know links won't always suit everybody. If you like our links please return to Atheism Wiki later when you've got everything you want from our links. If our links don't suit you you can come back to Atheism Wiki and look for something that suits you better.
- Religion Does No Harm, Bill Maher reflects Hilarious video