From my POV now (ask me again in 10-15 years, ill probably be eating my words lol)
Once they are about 16 or so i would have no problem with my kids having A drink while at home with me.
The reason i say this is because my mum and dad were very much against us kids drinking even though they got smashed pretty much every weekend with our neighbours!
So yeah my older sister and I rebelled and went out and drank at a friends house nearly every weekend - because we saw it as a novelty, something new and exciting.

Obviously my mum knows now everything we got up to when we were younger and i think shes learnt something because now she lets my brother have 1 or 2 drinks at family occasions and he has shown very good self control when he goes to parties etc.. he never comes home wasted only a little bit tipsy.

ETA: as for the drugs issue.. thats a whole other thread in itself lol.