Often, deep discussions about religion handle it as a collection of otherworldly ideas. But these necessary discussions seem irrelevant to many believers. They don't value religion primarily because of the many confusing details of its ideas, which they may not study seriously anyway (angels on pins, anyone?). They value religion because of its pragmatic impact on their everyday lives. They view religion as a cultural tool for specific purposes. Like pounding nails with a rock, the adequate usefulness of a tool like religion overpowers legitimate concerns about the tool's deficiencies.
In particular, throughout the history of civilization, religions have been tools for the encouragement of good behavior. As long as the religion was "proper", few objected to this traditional assignment. Even nonconformist writers, who mostly ignored religion in their own lives, nevertheless assumed that religiosity was essential to the ethical training of the lowly and bestial majority of society. Within prisons, clergy were welcomed as possible rehabilitation tools. In twelve step behavior modification programs such as "______ Anonymous" religiosity was one of the original tools. Schools included religion classes as tools for character development. Parents with religious childhoods, who may have stopped believing long ago, used churches as tools to ensure that their children absorbed the "right" cultural heritage with the corresponding baseline of behavioral expectations.
By contrast, a self-consistent atheistic perspective cannot link good behavior and the questionable ideas of religions. However, breaking the link implies a surprising compliment to the religious humans who consistently exhibit good behavior—who are good whether or not their religion's predominant morality agrees with them (perhaps they respond to the difference by creating a secondary form that's "reinterpreted" or "modernized" or "reformed"). If religiosity isn't a vital factor in their good behavior, then via process of elimination the vital factor is always them. The atheist can't give credit to their gods or to their religions. They may say that they're acting as an appendage of a divine compassionate being or that they're fueled by supernatural love. But the atheist must jump to the less far-fetched conclusion: they're just decent humans...who also are too hasty to accept statements about the existence of gods.
Consequently, the supposed religious basis of good behavior is instead a placebo illusion which yields imaginary additional moral fiber. It's ineffective apart from the believer's thoughts. It's akin to the trick feather in the movie Dumbo that the titular elephant holds while flying (tvtropes.org has alternative examples). Ultimately Dumbo realizes that the feather is a deception; Dumbo can fly without it. Similarly, to blame religion for genuine ethical motivation and determination is to act like Dumbo. Like Dumbo and the feather, genuinely ethical believers could be ethical without their religion. Religion can be a container or setting for describing ethics, but humane ethics aren't limited by it.
In reality, of course, modern decision-makers with faith-beliefs cannot face all modern ethical decisions through overstretched comparisons to ancient religious stories. That's why the more honest ones tend to mention "timeless principles" extracted from the religion, since the "raw" form contains ethical problems like toleration of slavery, religious-warfare, and inequality of all varieties. Religion is the Dumbo feather of ethics. It might be a helpful educational tool at first. Yet the one clinging to it is the real origin of all of its illusory ethical power. They cannot avoid ethical responsibility.