Doesn't that seem reasonable? Not in the extreme form you've taken at least, but in a milder form. It seems reasonable to me that a number of people who otherwise would not try heroin due to lack of access might try it if getting it becomes convenient enough.
It's naive to assume that just because getting drugs is relatively easy that making it easier won't increase the number of people who decide to use drugs. Just as it is wrong for prosecutors to bend reality to fit their interpretation of the facts, it is wrong of those in favor of drug reform to bend reality to fit their interpretation. I would love to see more reasonable drug laws, and I'm probably far more libertarian than most in what changes I'd like to see, however, I recognize that by improving access to drugs you probably will also increase the number of people who do drugs, all else remaining constant.