Ok, I don't want my 16 year old to have access to alcohol. Under your law, I would have to follow him around all day to make sure he does not purchase it. It would be similar to me trying to prevent my minor child from buying a snickers bar. If he wants a snickers bar, he will get it.
But say that you didn't want your minor child eating Snicker Bars, whose responsibility is it to prevent him from doing such?
Yep. Sorry, but the state is not here to do your parenting for you.