The anger is a "red vs. blue" mentality. They're Java developers, they always have been, and they always will be. They still think Microsoft--the EEE Microsoft of years past--somehow relates to their (Microsoft's) development tools and platforms org. It doesn't.
Things aren't "changing," they've changed already. .NET Core is more than stable enough to run on any major platform and has been for quite some time now. C#--especially the upcoming C# 8.0 with the new nullable reference types feature--is an excellent language that can handle anything you want to throw at it.
The hate comes from ignorance, pure and simple.