Once again, your views are subjective. What you believe the general concept of 'sin' to be may be vastly different to many other people. There is absolutely no way of saying who is actually correct, and any such judgement would be completely arbitrary.
I happen to think that much of what is presented as religiously based morality is actually rooted in practicality.
For example, sex outside of marriage is presented as immoral. The issue is not so much the sexual act, per se, but the potential results of it. Careless and indiscriminate sex leads to serious problems, so it is not a good idea as a practical matter.
I don't agree with you Joe that definitions of sin are completely arbitrary. Reasonable people can have a range of tolerance that may differ to some degree from others', but anybody with a semblance of a moral compass can discern right from wrong, at least on the extremes, based upon the ultimate effects of certain actions.
If I take a gun and indiscriminantly fire into a crowd, I don't think it would be arbitrary to determine that that is wrong. So I really have to reject your characterization of right/wrong and sin as arbitrary. I understand that you wish to look deeper for your reason to declare something as wrong than "it says so in the bible" but much of what is deemed sinful in the bible can be linked to painful and destructive results in the real world, whether a person is religious or not.
Your last paragraph actually sums up my basic belief, pretty much. I view morality as completely based on pure common sense, and
not what it might say in the Bible.
But that of course is also a subjective belief, and I'll readily admit that.
The reason for this disparity is that people do often have completely different views of what is morally right or wrong from the accepted norm. I could take an example of somebody more extreme than Opebo, who might believe that
to not commit murder, promiscuity, homosexuality, etc. is actually
sinful. As bizarre as it sounds, this is still a viewpoint. A subjective one of course, but then that is the central point.
There is simply no possible way to judge who is actually correct in their beliefs. Therefore, any such judgement is arbitrary.
(I typed all this up as Emsworth posted his reply. His view pretty much matches mine.)