How do you feel about teenagers drinking?

Do you outright forbid your teen to have any alcohol due to the legality of it in the area where you live, and if so, would you then be fine with them drinking if they were traveling abroad in areas where the drinking age was lower? I've been to places like the Czech Republic where it was perfectly acceptable for a 13-year-old to have a small gl of wine with dinner. If the law isn't your primary concern, what is? Would you allow your teen to have a gl of antioxidant and resveratrol rich red wine with a meal, provided that she won't be driving anywhere that night? Do you think it's acceptable for a 17-year-old who knows how to drink responsibly (never on an empty stomach; with plenty of water; only in moderation; and never before driving) to have one gl of wine now and then?