"Canvas"is the same word as "cannabis", just a different spelling, because that's what they used to make it out of. George Washington used to grow it.

"It's a way of blaming the victim" I'd have thought "addictive personality" is the reverse of that, being a way of saying people can't always be assumed to be to blame for getting addicted.

Whether it's personality or physiology involved I've no idea - but if you look at the way that some people can smoke tobacco for years, and give it up just like that, and others have enormous problems, it's fairly clear that we aren't all the same when it comes to getting addicted to some drugs - and it's definitely not a matter of stronger or weaker willpower.