You're misapplying the statement by Chief Justice McLachlin in this case. Engaging in sex with a person while they're unconscious is surely a sexual assault. But a naked, unconscious woman in the back of a cab doesn't equate to the cabbie committing a sexual assault. There would need to be evidence that he was assaulting her while she was unconscious, and that evidence doesn't exist in this case.

Why not convict the cabbie anyway? Because if you can convict someone of sexual assault without evidence or testimony that proves an assault took place, we'll all be the worse off for it.