Never said you had to do anything, but learning about other cultures, ie educating yourself, stops you from making comments that make you look backwards and stupid on public forums. Pretty sure you wouldn't do **** if a Sikh walked into your 'neck of the woods' and would be quite polite to their face, because that's how online anonymous cowards are. Everyone around you would be telling you to head for the 'airport' if you did.
PS I'm not a Sikh, but have lived within communities where they also live, and they are fine people, as are most 'foreign' cultures if you get to know them.
As I said above you could stab someone with just about anything pointy, which is what shivs are. Knife bans are not to stop people carrying knives for legal purpose, its to enable police to remove knives from those carrying them for the purpose of harm to others.