They are not saying you should do that for every child of couse but if they are going to parties with drink then to ensure it is controlled otherwise they will get hold of spirits etc (from parents drinks cabinets and so on) or way more drink than they could handle which of course is dangerous. I am talking 15/16 YOs not younger (so Y11 I guess).
Religion is totally irrelevant, if their beliefs mean they don't drink and the children follow the religion then presumably they also won't drink, that isn't banning it, it is a belief.
It is not the schools advice, apparently many schools are giving advice to say no alcohol at all whereas the professionals are saying if they are going to do it then to ensure it's controlled. I don't think I worded my post well, I definitely wasn't saying that you SHOULD do that for every child, sorry.
I don't think everyone teaches their children to drink sensibly, I think many people have their head in the sands, ban it or just don't care at all, all variations will have differing outcomes. We won't all get it right, there are several posters on this thread who have 2 or 3 DCs who are all very different.
Banning it may work for some, allowing a controlled amount may work for others. In both instances you will still get the extremes, I am not sure why you can't see just because it works for you it wouldn't always work for everyone.