An age-old debate
I'm not even sure if this is an issue in the US, but it's been simmering in Canada for years. My understanding, which may of course be flawed, is that the kirpan is typically small, dull and not much of a practical weapon. It's ceremonial, symbolic. A screwdriver snuck out of the school woodshop would be far more dangerous.
Multiculturalism takes on a life of its own.
I actually think that was the whole idea. Multiculturalism is a cornerstone of Canadian society, not merely something to be given lip-service when it's convenient.