I thinks underage drinking is stupid. Well, I think drinking in general is stupid, mainly because;
1. You don't remember anything.
2. You can't control yourself (I am lucky enough to be able to think [semi] rationally when I am drunk.
4. Drunk driving.
5. You have a (very) good tendency to embarrass yourself
6. In extreme cases, Alcohol Poisoning.
This is not saying I don't drink. Just that drinking in excess is stupid. That is probably why they raised the age limit. Too many people drinking in excess and doing stupid stuff (like drinking and driving).