Sin is not obsessively focused on the sexual. Sex is considered to be a gift to be enjoyed, for example, and the material world is always seen as good, as sacred. Sex itself is sacred and makes a bond between the participants which can last a lifetime. But we do many things that lead us to a state of sin. We turn aside from those we could sustain, we use the resources of the earth without thought, we ignore the plight of those who are persecuted, we blame others for our own faults and failures, we lie to ourselves and others...Certainly you can live a good life without believing in a god but where did the moral precepts you based that humanist life on come from? You don't have to believe in God, but the idea that humans are made in the image of God underlies our belief that all humans lives are worthy of respect and preservation. Removal of this idea lays us open to basing our values on feelings. Thus, we can say that assisted dying is a good idea, ends suffering, without understanding the pressures this idea puts on the old, the disabled, the sick, who may not want to die but can reach the point where they see themselves as a burden to be removed. That a life is sacred subverts the idea that someone can be a burden, or better off dead, at their very core. And that is a moral decision, but it is based on the idea that human life, all human life, is sacred. Which comes from the idea that humanity is made in the image of God.