Mace is prohibited in Canada, at least it was when I was wanting to buy nunchaku (numchucks). I found out that they're also prohibited, btw, but that was almost thirty years ago.
About the most serious self-defense item we can carry is a Fox-40 whistle. I had one blown in my ear (foolishly, not because of something I was doing wrong) and it slowed me down for quite a while.
I think it's quite okay for a person who feels physically threatened to defend themselves and slow down the "attacker" but only in the case of "clear and present danger". Unfortunately, that is subjective. I'd suggest that those who do carry mace, (or numchucks
) use it when there is a physical threat (not just verbal), a means of escape, and without any warning.
Just my ivory-tower opinion. I'm blessed not to have been in a situation (as an adult and Christian) where my physical safety was threatened.