Why do adults say that it is so bad to just chill with your friends and have a few beers?

I don't understand it, I'm 17 and if I wanna go have 4 or 5 beers with my friends, why can't I when it doesn't even hurt me? People call it binge drinking to have 4 or 5 beers within 2 hrs, but that's just normal drinking, jeez! Drinking adds a little more fun to it, and as long as we're not chugging 9 beers, then it really isn't a big deal. I'm not saying this because I got in trouble, because I never have, but I always see websites discussing ways to quit under-age drinking, but why? These are the days in our lives where we would like to have a little bit of fun before another 40 years of working in a small cubicle, cmon now society. I have talked to so many 30-40 year olds who say they wish they would have had a bit more fun in high school/ college, because they can't now. I'm really just confused on why people want to stop underage drinking so much when they should be focusing on "Driving under the influence" It really makes me angry when these websites try to make it out to be such a bad thing, when they never even experienced fun in their lives. As you can see, I'm pissed.