We can have a better discussion if we first recognized the circularity in our thinking the moment we say that sin is bad, evil, malicious, etc etc for then it now begs the questions what is bad, evil, malicious etc. And it is bad discussion because we get nowhere.
On the other hand if you say sin is not measuring up to a standard or missing the mark, or breaking or disobeying a rule or a law, that will be fine, if you can say at the same time what these reference is, and specify how you can know whether you meet the requirements of this reference.
For example you may say everyone knows or can feel what is bad, evil, malicious etc, then you are making the whole thing subjective, ie what is sin to me may not be to you, but that is a sound concept - though not necessarily true - namely that sin is a relative thing. Then we can go on to discern if this is indeed the case, ie establish its truth.
But if we cannot even get beyond knowing what we are talking about, then how are we ever to even start to know if this thing is true or not.