"Public" bathrooms, for example at Disney, are not on public land, so in fact, are not public. Many airports as well are owned or managed by private companies or institutions - the "public" arguement does not stand.
The people using these "private" bathrooms for these "roundezvous" are not the owners only. The bathrooms were created to serve the public who they have brought in. In fact, I believe the amount of bathrooms was regulated when they built Disney. The government regulates how many parking spots a "private" company needs. They regulate whether or not an elevator must be built for handicapped people. The idea that a business owner has full rights to use his private property any way he sees fit is an error. Once this owner brings people in, he/she brings government regulations in as well. My bathroom 10 feet away from me right now is a private bathroom. The moment I create a business in my own home with customers coming in, it becomes a public bathroom.