The Senate is institutionalized white supremacy https://www.lawyersgunsmoneyblog.com/2020/08/the-senate-is-institutionalized-white-supremacy

The most obvious way this is true is that it massively overrepresents white people: https://nymag.com/intelligencer/2020/08/senate-washington-dc-puerto-rico-statehood-filibuster-obama-biden-racist.html

But to build on this point, Republicans adding a whole bunch of barely-populated western states was not done merely for partisan reasons, but also for white supremacist reasons:

Backing up a bit, most of the framers of the 14th Amendment thought its most important provisions were not Section 1 but Section 2 (which orders Congress to strip representation from states that disenfranchise otherwise eligible voters) https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2483355

This was because they understood that no matter how precisely you worded the rights they would only be as good as the judges and legislators interpreting them. And from the Slaughterhouse Cases to Shelby County, this has repeatedly been proven correct.

But while Radical Republicans feared the civil war amendments would be gutted if Southern Democrats took over the government, the amendments were actually gutted by Republican judges, and Republican legislators refused to enforce Section 2. And this brings us to the Senate.

Stevens and the other Radicals weren't naive; they knew a lot of northern Republicans were not racial egalitarians. They expected Section 2 to be enforced not so much out of a principled commitment to political equality as to sheer political self-interest.

Because of the abolition of the 3/5ths clause, if southern states disenfranchised African-Americans and Section 2 wasn't enforced, as things stood in 1870 Democrats basically would have had a hammerlock on the federal government.

Expanding the Senate, however, meant that Republicans could write off the South and still be competitive. So the Senate is critical to explaining why Republican support for civil rights sharply attenuated after 1874 and vanished entirely after 1891.

In short, the only "norm" expanding the Senate would violate would be that in the past partisan expansions were done to exacerbate white supremacy rather than alleviating it. I don't think that's a norm worth preserving!

In conclusion, statehood for D.C. and a statehood referendum for Puerto Rico are not merely defensible but an urgent moral necessity.