Underage Drinking

I don’t understand how in the States you can enlist in the army or star in a hardcore porn video before you can legally drink. I guess you are not responsible enough to get drunk until you’re 21, but hey you’re 18 here is a fucking gun you have the power of killing someone. Or go ahead and star in a hardcore porn video and get hepatitis A through F. What’s the worst that could happen for younger kids to drink? Enlist in the army or star in a porn? And its not like you are preventing under age drinking. We all have older siblings or bad fake IDs. McLovin? On a side note the drinking age in Canada is 19, or 18 for our annoying French province Quebec.