Why is it an outrage? Are Mexicans some kind of Pariah?
It is an outrage because Mexico is a sovereign nation. Anyone coming into Canada from another nation should need a visa.
Jeez! Why not just do away with visas, passports, any kind of documentation? Just throw the border open and say, "C'mon in!" to anyone and everyone from anywhere!
I've never gone to Mexico but I would think you would have to have some documentation to get in there.