Sikh's carrying a knife, a bracelet, a comb, etc. has never bothered me in the slightest in all the decades I've known about this - the Khalistan movement in a particular location during a particular time aside, they're not exactly actual postcards for terrorism (despite what some might think when faced with people and turbans).
They always had a pass here in Australia for many years until things tightened up.
Not that I'm a fan, but in general Rules are Rules and making exceptions while fair in some senses will be unfair in others <shrug>.
Circling back to my initial comment- it is the case that there is an actual reason rather than a made up bit of bullshit, to reasonably suspect that a Sikh might be carrying a knife ... if they are they're almost certain to also have a comb .. so that's handy.
okee yeah, and rules are rules, and there's a reason to think that. It would be nice if we lived in a world where rules could be bent in some cases for individuals if they actually posed no theeat, but we all have to deal with the lowest common denominator wanting to cause the most damage, so here we are.
I must say, one thing that this reminds me of is what happens if you board an El Al flight. They don't racially profile you, they just ask you some fairly innocuous questions and watch your responses. I assume they have some way of monitoring your blood pressure, heart rate, and pupil dilation at a distance... but this hasn't really changed since the 1980s, when those things had to be read or guessed in realtime by a trained human. They have a phenomenally safe record, for a country under constant terror attacks.
My takeaway from flying El Al is that there is a much better way to deal with security, that analyzes and addresses the potentially bad individual motives of anyone getting on a plane, and mostly lets everyone else pass. Which is to say that security in its best form should be almost transparent to people without malicious intentions. Having good intelligence coupled with treating each person as their own potential bomb threat is far superior to superficially treating everyone as a threat and having no real security, and far better than just creating security theater around certain people because they're of one race or ethnicity. But El Al's methods probably don't scale well to the size of US or European air travel, because you need highly trained people to stand there in the airport make those calls on the fly for every single passenger.
If I were to guess - I'd guess El Al would let a Sikh bring a blade if they looked him in the eye for 10 seconds and decided he was okay.
The issue isn't really whether a Sikh might be carrying a knife (as Sikhs generally advocate non-violence and pacifism), but if an exemption is afforded to give Sikhs the right to carry weapons on a plane, whether a terrorist might then impersonate being a Sikh in order to get a weapon onboard.