If they have already developed the content, then it should be released with the rest of the game, for the price of the game.
Why? Genuine question. What does it matter to you as a consumer when the content was developed?
If the point you’re actually trying to make is “if the game is developed as a whole, but then content is carved out such that the base game then feels incomplete without it”, then this is already covered: a game which feels incomplete is inherently flawed, and so doesn’t justify the price of a full game. That’s my original point - most people are actually just pissed at inaccurate or unfair pricing, and DLC can enable that (but doesn’t have to), so they misdirect their anger to all DLC instead.