Religious believers often draw support from the fact that most of the world's people (about 80-90%) are religious, or at least profess to be. This argumentum ad populum (argument from popularity) is logically fallacious, but nevertheless does considerable work in propping up the faith of waverers -- we can't all be wrong! Actually, you can. Just a few centuries ago, nearly every human believed the Earth to be flat, and to be the central feature of the universe. To take a more modern example, Al Gore never claimed to have invented the internet, contrary to popular opinion. The word myth is in our lexicon for a good reason. While many widely believed ideas are true (George Washington was the first President of the United States), they are widely believed because they are true, not vice versa.
Furthermore, properly construed, popular appeal cuts strongly against the religious believer. While it is true that Christians, Muslims, Hindus, Sikhs, Buddhists, Taoists, and Zoroastrians believe in some form of a "higher power", their beliefs diverge widely from there, to the degree that they are often mutually incompatible. It is fundamentally dishonest for a Christian to count a Buddhist as a believer for the purpose of argumentum ad populum, while simultaneously embracing a theology that consigns that same Buddhist to hell (or at least denies her entrance to heaven) for being an infidel. The 2001 edition of the misleadingly titled World Christian Encyclopedia identifies 9,900 distinct world religions, not to mention the numerous denominations and sects the world's major religions have splintered into. When a Presbyterian honestly considers what portion of the world's population holds beliefs compatible with his, he will find himself in a distinct minority. That same statistic would look downright bleak were he to consider not just those alive today, but all humans who have ever lived. So much for popularity.
Popular appeal probably has its strongest impact on the local level. Most Americans find themselves in communities populated by believers, and the urge to fit is hard to resist. While many of us have a bit of a rebellious streak (some more than others), the plain truth is that humans are largely conformers. Many evolutionary biologists believe this to be an evolved trait -- conformity helped early human societies cohere, cooperate, and thrive. This helps to explain why many atheists and agnostics remain "in the closet" -- they want to be popular ,and to avoid the risk of becoming societal outcasts. This serves to entrench the problem, because by continuing to identify as believers, these doubters contribute to the perceived popularity of religion.
Once again, I ask the readers to my blog to raise their consciousness -- argumentum ad populum is doing some of the work to hold together the foundation of sand that religion rests on, and needs simply to be exposed. If the religious had a sound basis for their beliefs, they would have no need to fall back on logical fallacies.