Are the sex acts confined to the bedrooms or do they spill over to the pool and common areas (where other guests would be exposed to fluids and witnessing the acts)?
Does the jurisdiction permit sex dungeons and swingers nightclubs? Some swinger social nightclubs do not permit sex to occur on the property (although reports come in of people having sex in the parking lot in their cars).
These are the questions that need to be asked of prosecutors. As I say, calling this a "workshop" allows the banner of an educational seminar to blur the real purpose of the weekend. Early hardcore films purported to be an expose of the changing sex laws in Europe (with titles like "Pornography In Denmark"). The courts put out the notion that obscenity has "no redeeming social value" so the hucksters make it "educational".
The gatherings in SF and DC this past weekend were called antiwar protests but they were anything but if you bothered to watch. The language used defines an argument. Don't start yourself out in a losing position having to knock down straw man arguments.
The county health department already checks all the things you mentioned.And you are right about charging for entrance and it spilling out into the public then by all means deal with it with EXISTING OBSCENITY LAWS which were written with these very things in mind.No,instead of Missouri trying to enact morality legislation,enact legislation to do something about the meth labs that give the Show Me State one of its most dubious distinctions; the Meth Lab Capital.