My Mum is really conservative and quite anti-drugs, I think it's more that she had quite a strict and traditional upbringing.
My Dad not so much, I know he enjoyed acid when he was younger, and liked to experiment. He never smoked in front of me when I was younger, and I had no idea he smoked until the beautiful day when I found his. I was about 15-16 then and got a bollocking for nicking it.
It wasn't until I was 18 and I went for a weekend in Amsterdam with my friend, my Dad and my Dads girlfriend, after that whenever I have been to visit we both smoke, not in a "i smoke weed with my Dad" novilty, we are both adults, we both have the ability to make our own choices.
He has always been pretty open with me from the age he suspected I was using drugs. No bullshit, pretty much told me the facts. As a result I seem to be one of the more sencible drug users I know.