The constitutional question turns on this very narrow principle of justice called overbreadth, so if you can find one case where this would apply in a way where that person particularly would not be able to offend or would not likely offend, then the Supreme Court says that this is a violation of section 7 of the charter.
I've written as to why I think, in fact, that principle of fundamental justice is not fundamental justice at all. However, then it goes to the section 1 justification and the question we would have to consider is whether, by getting rid of the discretion that's been so problematic, catching the offenders who will fall through the cracks would be worth catching one of those oddball cases where we might be able to find someone who is not unlikely to reoffend.