PDA (public show of affection) -for highschoolers mostly?

Okay so im doing an essay on PDA (public show of affection) for my english cl. I think its really stupid how teachers yell at us for just hugging or kissing your boyfriend or girlfriend, and i get in trouble all the time. It gets really annoying. I just want to know what bad things and what good things are about PDA. I want your opinions about it. Thank you!