> That's pretty disrespectful and ignorant to other cultures and customs.

Not all customs deserve respect. I guess I don't have to produce a list of all the things that were once "customs", and that now horrify us. "Sir" is a honorific that implies class distinction, to indicate that someone is socially above you, by virtue of birth or by the decision of a monarch.

I know that the British crown now give knighthoods to honor notable artists, scientists, politicians, etc. It also still uses it in the traditional sense. In the UK, you can have a seat at the House of Lords (the upper house of parliament) because of your social status, either by birth or by position in the clergy. I certainly do not respect any of that.