Well, I wouldn’t go that far. Sure, they aren’t as good of a citizen as GitHub or some others. But until Microsoft started experimenting with open sourcing things, they wrote or purchased all their own code. Not many giants of the software industry can make that claim … as a matter of fact, I can’t think of any off the top of my head that are still relevant. That’s not being a parasite, that’s competing on their own merits.
Publishing things via open source is giving a gift to the world. It isn’t polite to give someone a gift and then turn around and say they should give it back because you don’t like how they used it.
And also, as anyone who has been in the open source community for very long knows, when you fork something … it gets harder and harder to integrate new stuff into it as the two projects diverge. Sure, they took Atom and built on it … but I’m confident that Atom is going to make great strides in the future. We’ll see if Microsoft learns that the biggest benefits of working with open source are gained by participating, not just taking.