I do understand what you are saying. Yet many things that are done in private are already illegal because of their negative impact on the individual and on society. You can't operate a bomb factory, even if you aren't selling your product and are only using it for your own personal enjoyment. The same goes for a meth lab. Or, much more appropriately in this case, a bawdy house. A sex convention is little more than a temporary brothel. I am sure that there are existing laws against this sort of activity in the jurisdiction in question. They should be enforced.
Tying up my wife and spanking her is not.