Although there are billions of people throughout the world that participate in religious cultures, there are still large communities of people who do not agree with the concept of religion and believe it to be detrimental to society or fundamentally silly. Some people argue that religion should not be taken seriously because of how many religions have come and go. There are some religions that were once believed by many people, but are now viewed as "myths." What separates these outdated religions from the religions that are currently practiced today? Some people simply do not believe religion should be taken seriously because there is no tangible evidence for the things that religions claim to be true. Science cannot prove religion. Some people argue that because no religion is universal, none of them can actually be true.
There are many more arguments against religion of course.
It would seem that there are many more people who are affiliated with some type of religious practice than those who are not--and this is true. But the number of people who identify as having no religious affiliation is growing. No religious affiliation/atheism/agnosticism is now the third leading "faith" across the globe.