Because, It's Wrong!
A statement I have heard many times and one that I feel says more about the person speaking the words than the action they are describing as wrong. We all have unique life experiences and all develop things that are "right and wrong". These are more about ourselves and our own desires for our life than they are about the correctness or incorrectness of anything. To become free of feeling that things are wrong, maybe allow that these things are NOT what I choose for my experience and allow what is to be.