I like this cartoon, from the creationist organization Answers in Genesis. It expresses a conservative religious concern about the source and authority of morality very well.

If there is no external, transcendent, supernatural, absolute, objective, (insert any other hardening adjectives you like) source of rules, then people are just making the rules up. And if so, what stops someone from adopting self-serving, community-exploiting “rules”?

It’s a good question. Nonbelievers have to spill a lot of ink trying to answer it. I don’t think we do a bad job of it—certainly not compared to the authoritarian nonsense a cartoon like this is actually defending. But the secular, humanistic ways we figure out how to regulate our lives together are also complicated, ambiguous, imperfect. They’re hard to put in a cartoon. Compared to the visceral appeal of God-given rules this cartoon expresses, the secular version has to labor against a intuitive disadvantage.