Clearly Adam's sin in the Garden of Eden affected everyone. And clearly if you murder someone, or commit adultery, it affects others. But are there sins which do not affect other people?
What I am wondering for this question is if every sin affects other people.
As an extreme example, suppose God has spoken a promise to me, and I doubt it for a moment, but then repent and have faith. During my time of doubt, I never speak or do anything - it is all internal. Would that sin affect others?
The reason I am asking is that often times, non-Christians define "evil" as that which does harm to another. By this definition, they justify things which are explicitly forbidden in Scripture, because in their eyes, it doesn't affect anyone else. I also often hear Christians define "sin" as that which does harm to another. One of the many passages used to support this teaching is:
Love does no wrong to a neighbor; therefore love is the fulfillment of the law. -Romans 13:10
Is "evil" defined as "that which harms another"? If not, it seems like Christians need to stop using this secular definition in their teachings.