For the same reason you can't invent a new kind of pain killer and tell doctors and patients that it's less addictive than the existing alternatives, when you know for a fact that it is far more addictive.
Unless your primary goal was to kill the industry, and never really had the victims' best interests in mind at all.
Taking a long view, one could argue that there will be less victims overall. This isn't to say that I'm in favor of making any drug illegal.