The reason D.C. should not be a state today is the same reason why it was created in the first place: so that Congress and the Federal government would not be under the undue authority or influence of any state. The constitutional principles of federalism and the separation of powers are fundamentally incompatible with D.C. statehood. Federal actions and officials must be independent of state governments and not unduly bound by any state's particular laws. One sovereign cannot live in the house of another.
Both federalism and separation of powers are threatened by deep institutional rot and DC statehood would hardly change any of that. Invoking ether of these two as plausibly threatened by DC statehood is trying to protect a false ideal.
If admitted, the Douglass Commonwealth would be grossly unlike any other state in our nation, either historically or today. The federal government is not a visitor upon D.C., the city has grown up around and entirely dependent on it. It has no identifiable history or economy other than surviving off Federal tax receipts. It is only 5 percent the size of Rhode Island. It's 100% urban population would not be home to a single farmer or miner. As a state, D.C. would be the richest yet have one of the highest poverty rates, simultaneously the most educated yet with the worst high school graduation rates. Admitting D.C. as a state does not improve upon what some proponents of the idea claim as the great failing of our U.S. Senate - there it would elevate a small, idiosyncratic enclave to the same level of huge, diverse states home to tens of millions.
I know I'm going to get Gish galloped in response, but this paragraph is crazy. There's no reason other than institutional momentum that either historic or modern concepts of "states" as places full of miners or farmers (??) are worth protecting at all. If anything, a useful Senate would have
more representation that is designated explicitly for urban areas.