Divine forgiveness and atheist morality
Understanding their perspective starts from what is usually seen as the happy fun part of Christianity, the part that is relentlessly pushed as Christianity's "good news": God's forgiveness. In orthodox Christianity, all of our sins can be forgiven by God. But making our sins forgivable by God requires making God the primary victim of our sins. After all, it's the victim of a wrongdoing who can forgive it. If I hear that my friend cheated on his wife, it would be silly to say to him "don't worry, Bill, I forgive you." Certainly I can decide whether or not I will hold his adultery against him (in terms of deciding to stay friends, etc), but that doesn't address the wrong he did to his wife. Only his wife can give him forgiveness for the harm his cheating did to her. She would -- rightly -- laugh in his face if he said "give it a rest, honey, my friend Stentor forgave me for cheating on you." And this fact is not changed by the forgiver being in a position of authority. If one of my students steals another one's textbook, I can't forgive the first student on behalf of the second.
If God exists, he could forgive sins that are against him. He could forgive blasphemy, and failing to worship him correctly. He could even forgive the hurt he suffers when he sees us sin against each other. But he can't forgive the hurt one person causes to another -- unless that hurt doesn't exist, and only the harm to God is meaningful. If our sins against each other are sins not because they hurt another person, but because they contravene God's law, then God could conceivably forgive us for everything. In this God's-law scenario, God is the only victim and therefore the only one whose forgiveness is needed.
Todd Friel, the host of "The Biggest Question," is quite explicit about this. He tells us our sins really are primarily affronts to God. Kirk Cameron ends up emphasizing the point in his explanation of why our sins deserve infinite punishment in hell. He imagines lying to various people. If he lies to his young daughter, there's nothing she can do to him. If he lies to his wife, who has more power, she could make him sleep on the couch. His boss could fire him, and the government could put him in jail. By extension, God -- whose power is infinite -- can justly give you an infinite punishment for lying to him. This is a very blatant might-makes-right view, in which the badness of an action is proportional to the power the victim has to punish you. Cameron believes that, were lying to his daughter not also a sin against God, he could lie to her with both practical and moral impunity because she lacks the power to punish him.
If this is "true" Christianity (obviously it's just one strain, albeit a very popular one), then I have to say I'm an atheist because I care about people. Other people matter, and they are the real victims of the bad things I do to them. Were God to appear and tell me I'm forgiven for my sins against other people, I would reject his offer, because I believe that forgiveness would be fraudulent. If I hurt another person, only that person can forgive me. Friel and Cameron have trouble with the idea of morality without God because they think the only kind of immoral behavior that exists is wrongdoing against God. I think morality without God makes perfect sense because I care about how my actions affect other people. All Friel and Cameron do is show that there's a danger that belief in God could distract you from caring about other people.