I think at least part of the problem is that there is a tendency to think of particular sins rather than sin generally. Is God concerned only with certain specific sinful acts when He says in His Word, "The wages of sin is death"? A second tendency is to think of the worst sins as being those that get the sinner into the secular headlines and courts. What do I mean by that? Well, when did you last see a headline in a newspaper that said something like: "New York Man Covets His Neighbor's Wife", or "London Woman Does Not Love God With All Her Being", or "Youth From Ottawa Refuses to Believe on the Lord Jesus Christ"? (Please don't read anything into the place names - they are just examples
).
Far more important is how God views things.
As for the idea of dancing being sin, surely it depends on various things, like who you are dancing with, the nature of the dance itself, and so on. Dancing
per se is not sinful.