I'm not in favor of scaring a kid to death, but I think it depends on the kid's personality, maturity level, ability to handle information, and penchant for rebelliousness - i.e., there will always be kids that you can tell the truth and explain carefully that you don't want them going out and doing this, but if they DO choose to for some dumb reason, you want them to know the facts and how to prevent unwanted things ... and all they're going to hear is "no" whereupon their response is going to be "YOU SAID NO! IMMA GO DO IT NOW!!!"