If you really think about it, Poison is very offensive outside of Pokemon.
It is dangerous and can cause a rather painful death.
Thinking like that, Poison should be Super Effective against more types, although there isn't a snowball's chance in hell that this will happen.
There are a few useful Poison types that do quite well in OU:
Obviously there's Gengar, Roserade and Tentacruel, but what about Crobat.
Nidoking, Nidoqueen and Drapion are pretty good Pokes in my opinion and are used fairly often in UU.
Anyway, at the end of the day, Poison is just horrible as an offensive type - fact. This thread's purpose was not to demand more SE damage for Poison, it was merely to discuss its flaws and how they COULD have been improved. Poison as a secondary type usually works quite well, the Fighting resist is always useful although the Ground weakness it not so great.