This is a good question and I've got a good answer. A couple of good ones actually.
First, no, nobody's supposed to shave their pubic hair any more than they're supposed wear the hair on their head only one special way. Can you shave if you want to? Of course! Do you have to shave if you don't want to? Definitely not. It's strictly a fashion thing and that makes it your choice! (This would be a good place to note that for more than 100 years before the late 1980s Westerners believed more rather than less pubic hair was sexy -- back then the peer pressure was against shaving! It was still a fashion decision and therefore still a personal choice.)
Now, secondly, you asked about shaving before sex. If you mean right before sex I'm going to say no, definitely not. Even assuming you don't get nicks or inflamed hair follicles, shaving can create tiny abrasions that make it easier to pick up infections from a partner's skin -- not just sexually transmitted infections, but also plain old everyday infection infection. (It doesn't even have to be sexual contact to spread infection, by the way. Doctors traced a pretty serious outbreak of disease-resistant Staph infections in a Connecticut college football team to a practice of body-hair shaving before workouts!
So. Bottom line? Shave if you want to, don't if you don't -- that part's up to you. But if you're going to shave a body part that's going to be in very close contact with other people's body parts you're probably going to be better off planning enough ahead to let those micro-abrasions heal.
Oh, final notes: Human beings have been around for thousands of years, maybe over a million years! How long have we had razors? Not that long, right? And if humans didn't die out in all that time then while we might choose to shave today we're obviously not required to.