Religious believers tend to associate their religion closely with morality. Some go so far as to think that the two are inseparable -- that without their religion, or religion generally, or at least some sort of theism, morality and moral behavior are impossible. Depending on their attitude, this can lead people to insist that unless a person is a member of their religion, or is a member of some religion, or is at least a theist, then they cannot be moral and if they are given any power then they will end up promoting immorality.
These attitudes are exhibited to one degree or another by many on the Christian Right. Christian Nationalists in particular act like their religion is necessary as a moral foundation for America and, furthermore, that all of America's ills can be traced to people's failure to uphold traditional Christianity. Atheists especially are targeted for criticism -- not only do they reject Christianity and likely any religion at all, but they don't even believe in any gods.
In fact, atheists are sometimes approached by apologists with the argument that atheism is incompatible with morality and, therefore, that the need for morality is a good reason to become a Christian. They don't realize that even if there were no reason to be moral in the absence of any gods, that would at most provide a prudential reason to believe in God. This cannot support the claim that some god actually does exist. If morality requires a god, and there are no gods, then we simply have to live in a universe where there are no absolute, independent moral standards and where we have to make our own way.
Some on the Christian Right even take advantage of tragedies to make both of the above points. School shootings, for example, lead some to argue that the absence of morality is due to the absence of Christianity, that atheists and secularists are the cause of all this, and finally that atheists should convert to Christianity to stave off future tragedies.
This image is based on a World War II poster depicting a soldier telling workers at home not to get hurt because they are needed on the job full time. It is similar to a real ad used by Answers in Genesis which depicts a child pointing out gun at the viewer. Accompanying the image are the words "If you don't matter to God, you don't matter to anyone." The implied message is that without God in our lives, nothing matters at all and this causes us all to descend into barbaric violence.