700,000 Americans live in Washington, DC. They pay federal taxes, serve in the military, and yet have no voting representation in Congress. DC has more residents than Wyoming or Vermont, both of which have two senators and a full House delegation.
The argument against DC statehood is nakedly partisan: DC would elect Democrats. That's not a constitutional argument. It's an argument for permanent disenfranchisement based on anticipated voting behavior.
DC should be a state. The people who live there are Americans and Americans get representation.