Myth:
Because atheists abandon belief in the God who provides standards of objective truth, they are capable of accepting any nonsense as if it were truth. Consider the wise warning of G.K. Chesterton: "When people stop believing in God, they don't believe in nothing — they believe in anything."
Response:
Many religious theists think that their God creates or otherwise provides a set of objective standards against which they can measure all their beliefs, attitudes, behaviors, etc. Without their god, they can't imagine how anyone could possibly differentiate true from false beliefs, moral from immoral behaviors, proper from improper attitudes. Atheists who don't believe in any gods are thus capable of believing and doing absolutely anything, having nothing at all to hold them back.
Religious theists use this myth as a way to deny that atheists have any sound reason for morality, for believing true things over false ones, or for being able to deal with life while holding on to the proper attitude. If religious theists can be convinced to believe this myth, they can be convinced to dismiss both atheists and atheism as having anything positive, useful, or interesting to offer anyone. It says absolutely nothing about whether any form of theism is more likely true or not, nor does it say anything about whether atheism might be a more reasonable and rational position to have. Instead, it's just an attack on the supposed consequences of atheism in order to scare people away.
There is a small grain of truth buried within this myth. Atheists are not bound to believe the things which theistic religions teach as dogma, doctrine, or absolute truth. Atheists are not bound to reject all the things which theistic religions teach are sinful or false. In a sense, it's true that atheists are able to believe many things — certainly many more things than most religious theists. What's not true is that atheists will believe such things because they have no standards. Not having someone's god to define standards isn't the same as having no standards.
As to what those standards are, the answer will vary from atheist to atheist. Most skeptical and scientifically-minded atheists in the West will tend to rely upon reason, logic, and science. This is basically what defines a person as a freethinker, and while being a freethinker isn't the same as being an atheist, it is true that freethought is quite common among atheists in the West. Other atheists will rely on different standards, like insights they derive from Buddhism, meditation, and other religious traditions.
Now, religious theists who object to atheism and atheists may not accept these standards and may even have valid objections to at least some of them. Disagreeing with the standards is not, however, a justification for saying or even implying that no such standards exist in the first place. Given that atheists do have standards, it's not true that atheists will "believe in anything." Given how obvious it is that atheists do have various sets of standards, there's no reason for religious theists not to know this — and thus no excuse for claim otherwise.
G.K. Chesterson wasn't offering a warning or providing any insights into atheism. At best, he was simply making a logical fallacy known as argumentum ad baculum — an "appeal to force." Chesterson was making an argument against atheism not on the merits of religion or theism, nor on the basis of there being anything false about atheism itself. Instead, he was trying to scare people about its alleged implications, none of which he could show to be true and all of which he had to know were founded on falsehoods. He couldn't have not known that atheists do have standards, even if he disagreed with him, so by implying that they had none he was doing no less than bearing false witness.
