I'll tell you why, because loads of people don't have a mind of there own that's why they say such foolish things, their only following and parroting traditional authoritative societal thinking, they're to brainwashed to dare step out side the limited box of their enclosed reality to see the bigger picture of true reality, which only limits their experience's and their cognitive growth therefore limiting their ability to reason to a higher potential.
In other words most people speaking against kids kissing, kids dating or having sex with adults or 18 year old men/women dating 50 year old women/men, are people who have never been in or experienced such relationships therefore their opinion is of no credit to anyone but themselves because it is totally illogical for someone to give an opinion about something they know nothing about or haven't experienced first hand....so you don't need to listen to the nonsense that comes out of these peoples beliefs. 12 is not to young to share kiss's with someone you feel love, lust, infatuation or just whatever make you wanna kiss someone!