I agree, except that the fixed resource is votes, not economic resources (which everyone here knows are not fixed in any practical sense).

Democracy is a vote market, and strong identities are the strongest persuasive tool available for acquiring votes. Strong identities we know of are skin color, religion, and universalist ideologies (think communism).

Once a particular identity, or combination of compatible identities becomes large enough to have a chance at becoming a winning coalition, the logic of the democracy market almost guarantees it will be deployed for that purpose. Even in the absence of underlying economic factors.

TLDR; democracy has a lot of very scary failure modes, and the US has been lucky to avoid them because until very recently, there haven't been strong competing identities, so people have been free to argue over tax rates.