The thing is, a lot of the people opposed are (I'd imagine, anyway) opposed for economic reasons rather than "moral" ones. Would you let the head of a rival company help you design your products? Wouldn't you just end up with a load of ****? Such people shouldn't have been involved in drafting the law.
There'll always be people opposed, but I don't know. I've seen a few American anti-marijuana campaigns, and while I don't know how widely they're believed, I think they're portraying more and more ridiculous ideas of what marijuana does. The trick is word-of-mouth. My parents were around in the 60s and 70s, and at a certain point we both came to the realisation that it would be pointless for them to pretend that they hadn't used marijuana, and pointless for them to lie about it. But that's how America seems to be working. Personally I wouldn't vote for someone who said they hadn't used pot in school or university, not because I support marijuana but because I don't really like to be lied to. If the admitted drug use rate in Parliament was anything like the drug use rate in society as a whole we wouldn't have a drug problem, which tells me that someone's talking ****.