Monuments and public celebrations are always political. Even your town’s Fourth of July parade is a staged political event. Now, "political" doesn’t have to have a negative connotation (who doesn’t love free candy and bead necklaces on the Fourth of July?), but in this poem, the State is a creepy, manipulative bureaucracy that is most concerned with preventing oddballs from getting in the way with the status quo. So they have created this expensive marble monument to the blandest person in the country, the one least likely to mess things up for those in power. The inscription on the monument – the poem – tells us almost nothing about the man to whom it is dedicated. It tries to convince the imaginary reader to be more like the Unknown Citizen.
Despite the poem’s sinister tone, there is no reason to think the Unknown Citizen is being manipulated by anyone.