And as property it belongs to the state, not the citizen. You are required and expected to have it on you at all times. You are also required to report it missing.
When I moved to the US, I was baffled that IDs are basically just driving licenses and you only have them if you... well have a driving license.
I guess it's about where you draw the line in the end. I understand that many US Americans feel threatened by the federal government as it is perceived autocratic to be forced to carry a government issued identification card at all times.
For me, it just guarantees that it is harder for someone else to walk around and impersonate me with some shitty fake ID.