Given the history of violence by and against Sikhs in this country, I'm in favour of allowing them to continue to carry them as far as it's safe to do so.
I'm not sure that is a strong reason to support the ability for one group to carry what are, in effect, weapons. I think there are plenty of other groups that will have suffered violence in a similar manner and we wouldn't permit them the same ability. And in a broader sense we look to use other mechanisms to prevent people being victims of violence that don't involve people being allowed to carry weapons in, potential, self defence.
So an argument on the basis of history of violence and self-defence seems particularly weak to me. And argument that it is a reasonable tradition is stronger, but you'd have to ensure that you are treating any groups that can claim they have a traditional right to carry weapons should be treated equitably.
That said, if the justification for carrying them isn't explicitly religious - superstition, as some might be inclined to term it - then how is it any different from anyone else carrying a knife under the auspices of 'self defence'? So far as it's a religious expression I see the justification (I think it's a little silly, but given that the evidence suggests it's harmless there's little point in arguing about it) but if it's not that, then why do Sikhs get to carry a knife for self defence but inner-city youths (of other or no religious persuasion) don't?
O.
I don't think it is being justified on actual self-defence grounds - rather it is being justified as a long-standing tradition based on a prior history of the need to carry weapons due to self defence.
But this is where the nuance becomes important - what justification is strong enough to elicit a special privilege. I don't think 'cos it is about religion' cuts it as the equality legislation is about religion OR belief (including lack of) - so a religious belief, in equality terms, should not be considered to be more important prima face than a non religious belief.
So a long-standing cultural tradition clearly associated with a particular community of group would (or should) be just as justifiable, or not justifiable, regardless of whether it is justified on the basis of a religion or culture but non-religious.