There are plenty of people way past the age of 18 who do not act sensibly nor as an adult. That does not mean they need a chaperone. You have to delineate an age at which people become responsible for themselves.
Whether adults act sensibly or not is not germaine to the topic here. That is like defending Michael Jackson by saying a lot of African American men do not molest children. What does one have to do with each other?
This was a high school trip where they were supposed to be watched, where drinking and gambling should have been not only discouraged, but punished.
Once they are out of the parents' home they can screw, get blued and tattooed. That is what the real world is for.