I think religion is absolutely a huge factor in happiness. Some of the most deeply religious people I know are also the happiest. Conversely the most miserable people I know are not. Most religions erase uncertainties & fears that haunt us, like death of loved ones and our own. They give people purpose and a reason to live — the sense that everything will be fine in the end. I don't like when people dismiss religion and liken it to fairy tales or delusion. At a fundamental level religion is perhaps the most effective antidepressant.