The problem with this isn't the skinnydipping or the other shenanigans, but the fact that the participants have the nerve to describe this as a "fact-finding mission" - which we all know is a euphemism for having lobbyists pay for all the booze and swag you can get.
I've been to Israel before. I didn't feel the need to take off all my clothes.
This was an AIPAC funded vacation for the Congressmen and their wives. This would probably be considered very unethical in many other countries.
Those Congressmen would probably be arrested in other countries.