i agree that the "cool" factor of it would go down so much. Now it takes at least some effort to drink underage which makes it feel rewarding, which really makes no sense to me, but whatever. If lowered, I think for maybe the first few years it would be a big problem as kids get used to the change and would go out and buy/drink just because they can, but after awhile,the novelty of that would die off.
Myself, I'm a French-American, and I've always been allowed to drink at least a little bit of wine etc over there for as long as i can remember. It does have an effect. I was taught to drink by people who respect and enjoy the drink, so it rubbed off on me and i'd rather just enjoy maybe one or two than have a shitload, but not remember any of it.
But I don't know, thats just me, I have no desire to just get completely drunk, and i don't really get why most people my age do.