Please understand that the suggestions below are some things that come to mind about the issue at hand, and are not at all my judging you because we have a few different ideas. I suggest them in a spirit of hoping to improve the quality of the form of questions here, not to try to exclude your questions!
Also in reviewing these, there does seem to be some inconsistency in what survives and what gets closed. I think we're all still trying to sort out what does and doesn't fit the format here and we're still not very good at it. Here I suggest some issues that might apply to your question, but some of these are also issues on other questions including my own foray into the topic.
One thing that caught my eye in your question is that it opens numerous different angles and thus leaves it open to being a thread that draws out debate rather than coming to a conclusion. For example you lead with a premise that the practice in question doesn't hurt anyone else. Whether it is or not, that is one whole like of questioning that would need to be dealt with. Next you lead with your own definition of sin and ask for answers to work from there. I for one would disagree with your definition, thus making it a very difficult question to answer without dragging it off-topic. Lastly, you ask a why question about God that would be much better generalized as a question in itself rather than launching it from this controversial issue.