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

2. You absolutely don't understand or are being willingly misleading about this "centralization" issue. There is quite simply no other choice but for us to support a centralized (read unique) consensus code. That's pretty much the only way Bitcoin works. It happens that the core developers have historically been the one trusted with maintaining this code and updating it. Several implementations have been built around this consensus code. Most of them have little support for very valid reason: their implementation is generally considered less tested and therefore potentially less secure than core implementation. Now should we blame core for attracting the most competent developers in the space? Would it be rational to ask of them to each start dividing their work between different implementations just for the sake of "decentralization"?

The centralization issue you refer to is nothing more than a lack of man power. That is, only a scarce amount of people are reliable and technically able enough to handle the highly fragile development of Bitcoin. It is no wonder the guys currently leading core are some of the world's most advanced experts in their own field. This expertise cannot be easily replaced or dismissed "because decentralization". It is absolutely unproductive and irresponsible to try to advance decentralization of Bitcoin development by encouraging incapable people to start messing around with their own implementations and risk breaking consensus.