It's a sexual fetish, most people know that. Is what they did OK to do in front of children? Would it be allowed in a school? What about a shopping mall?

I expect they would get kicked out of most businesses, public areas, etc. Most people would be uncomfortable being around them, whether they say anything or not is irrelevant. I wonder how many people on that plane were disgusted by them, I wonder how many complaints were made.

I'm shocked the airline let them board like that. People have been kicked off their flights for much less than that. Allowing passengers like this could cause the airline to lose passengers in the future, I would likely go with a different airline in the future if I could after seeing that shit. You have a right to many things but businesses can and do set criteria for customers. You ever seen a "No shirt, no shoes, no service" sign? Maybe a "No face mask no service" sign?

What they're doing may not be illegal but it doesn't have to be illegal to be disgusting/inappropriate and you don't have to break a law to be denied service, some things are protected but public display of your kink is not. Shame on them for subjecting the public to their kink and shame on the airline for allowing it.