What is wrong with the goal of decentralizing development across multiple competing implementations?

Nothing, but that is absolutely not what is happening. I know this is your new talking point Peter but it doesn't reflect on the situation at hand:
A totalitarian power grab for the governance of Bitcoin. Not the proposition of a new implementation but an attempt a hijacking the consensus code behind political motives
It IS a proposition. No one is being forced into it. Are you?
Of course not. But in typical dictator fashion they have managed to use their authority, PR & industry relations to instill false expectations into more simple users and steer the masses to get behind them against a "common enemy" on the premise of "inclusion" and general abuse of the sever misunderstanding of your typical redditor.
They absolutely have a right to release different code but it should stand on its own and not require a complete propaganda campaign.