Yes. Although most identification cards cannot be used to prove citizenship, they still play an important role in the first steps to identifying a person as a citizen. ID cards can be carried to simply show that a person lives in a particular city, state or country, and since they are exceedingly more difficult to fake these days, I feel they pose as a satisfactory measure for citizens to uphold their identity.
Yes, ID cards help citizens uphold their identity because having a physical representation of that identity on them at all times demonstrates to other citizens, officers, and elected officials that their identities are valid. Though one has a right to be taken at one's word as to one's identity, an ID card is a definite help.