Religion appears to have mass numbers during times of intense turmoil. War, famine, and other things that are considered to be the opposite of happy times. So basically, religion flourishes when people are unhappy.
Does this imply a link between religion and unhappiness? Possibly.
Currently we are in an age where you can do what makes you happy, to an extent. We also have the largest number of agnostics, atheists, deists etc. who are not affiliated with religion. Are people becoming less religious as their standard of living and thus happiness are improved? Or is correlation not necessarily causation?
Is in the amount of suicides and depressive disorders among their citizens. Research from the Mayo Clinic of Minnesota recently showed that depression and suicide was up 25% in non-religious nations as compared to religious nations.
Atheists are more likely to self-harm or to have depressive disorders than the religious, acording to numerous studies and research by medical preactices throughout the globe.
...Coexist by their very nature. While Christianity does have a moral code within it's doctrine, those rules are in place to protect the individual from their own selfish destruction. They are not meant to impose some sort of monastic lifestyle. There are very real temporal consequences to making poor decisions and living selfishly. By being freed, through Divine intervention, to live selflessly and focus on the needs of others brings personal joy and a sense of higher purpose and belonging to a community.
Being without that moral structure and Divine strength to abide by it, leads one to find happiness in selfish and sometimes destructive desires. When one is concerned about their own happiness and not the needs of others, the damage their communities and the relationships they could have enjoyed in life.