If you want to have an entirely separate argument about what Core do with their code, you're more than welcome to. They are free to publish whatever code they wish and no one is in a position to stop them. They are also free to accept or deny code contributions from any individual and no one is in a position to stop them. In fact, I'm pretty sure we agree on that part.
But the argument you originally made is that Bitcoin is not a free and open market. This is disproven by the simple fact that there are competing Bitcoin protocols right now. Anyone is free to release their own implementation of the Bitcoin client with any modifications they so choose. If the market decides overwhelmingly that the modified code is superior, that's the code Bitcoin then adopts. It's beautiful. I wouldn't change it for the world.
Carefully worded, but not a true description of what's really happening.
Describing the fork clients as "competing" protocols implies there might be room for whichever protocol loses the competition. You know as well as I that there is no 2nd and 3rd place if you fork the Bitcoin network to a different protocol, so it's a zero sum game. This is
not equivalent to a free market competition, as there is only one bed to sleep in. It's equivalent to a majority led compulsory purchase order "not your house any more, get out". Your argument is wrong, it does not observe the free market or property rights.
If you were really interested in an actual free market, you'd be arguing for a scenario that actually conforms to free market dynamics. Stealing someone else's project doesn't count.
If there is a fork, the "losing" side is free to join the new consensus and propose revisions of their own from there. Protocols can perpetually compete assuming developers don't decide to pursue a new, incompatible chain and create an altcoin. You know, that thing you're currently encouraging developers of alternative clients at the moment to do. It's not "stealing someone else's project", as the developers of alternative clients are simply publishing code. There's no identifiable act of theft within that process. Also, it's stated on just about every Bitcoin related resource that no company or individual is in control of Bitcoin. Ergo, you can't seize control of something that no one directly controls. Ultimately it's up to the miners and node operators as to whose code governs the protocol.
Also, it's irrelevant whether you agree with me or not, because it's not going to change the fact that we have a free and open system where anyone can modify the code as they see fit and users are free to run whatever code they want.