Sin is False Morality

Sin is often a moral act, it's just that the morality is a bad one. For instance, lust as a necessary thing for people to engage in in order to pursue mating partners so that their genes get passed on. It's extremely important that genes get passed on, so much so that men have to stare at every attractive woman who walks by, just in case it's an opportunity to pass on the gift of life.

Anger is necessary so that we can defend what is ours. It's extremely important that we not die -- we are the precious gift of life that is our responsibility to not lose -- so much so that if someone even gets close to being close to threatening a resource that might somewhat prevent our deaths, we must become angry -- just in case that's the critical thing that is the cause of us living an extra day or week or even month.

(Any other sin that can be linked to self-interest works similarly.)

When we make idols out of people or things, then we are being moral -- the morality of worshiping false gods.

Satan tempts us to be falsely moral, using responsibility.

There are theistic worldviews and atheistic worldviews. According to atheistic worldviews, there is no God to help you, no God to trust in. You have to take care of yourself. If you do wrong, you have to take responsibility for what you did, because there is no God to make everything right in the end. So your mistakes will never be covered over, and you need to always get things right the first time. Being very responsible in an atheistic way takes us away from trusting in God, because we must be in control of our own (or others') well-being, not letting God be in control. But in order to be responsible to God (to "fear" him, perhaps), we need to trust him. His reality calls for us to trust, so we need to respond in trust. Trusting God can be a deliberate, ethical act.

Being responsible to the wrong morality is potentially worse than to be irresponsible, although that also can be bad.