Gross sin? Lolz! Gross sin for those guys is sexual. Like Judah out looking for a prostitute to have sex with? That was fine. I know, Lots daughters having sex with dad? That was fine too.
These numnutz don't know what "gross sin" is. For Christians it's denying Christ. Paul is the one babbling on about sex all the time & that's because he was single and hanging around Hellenistic Greek society.
The original sin has nothing to do with sex; it was THEFT.
Leave it to the GB to take something Christ used to denote good and make it denote bad.