When we live in a culture we strange other cultures, isn't it?

I never understood why people gets upset when an exchange asks your ID. This is because in my country , within UE, i can be arrested (for a couple of hours) only because i don't carry my ID documents (nationality and driver license) when i'm on public places (streets, sidewalks, etc). If an officer stops me and asks for my ID i have to show him my documents. It's simple as that...