The considerate seafarer might consider warning others, rather than sitting back with popcorn. All these arguments really center around two points, will the mermaids eat you, and even if they will eat you, should we care that the singing tricks people or just accept it?
Watching theses events is like this famous passage of the Odyssey. Once you are tightly attached, and don't risk to go overboard (and start buying stuff you don't really need), then enjoy the show. I've been told their exciting song is the most detailed and beautiful thing you've ever heard :)