Presumably they feel the same way about all closed-source browsers?
Also, the comparison to Flash is not quite right. For example, Flash was an entire black-box, top to bottom, with a runtime, codecs, UI, a JS engine, etc., which downloaded code from the internet to run it.
Web DRM, on the other hand, is a standard that allows for an encrypted video stream to be decrypted. The only differences that I can see between this and the current state of web video are that now the stream can be encrypted. Everything else is still using Javascript, HTML, CSS, HTTP, h.264/265, etc.
The thing that gets me is that open-source browsers are free not to implement this extension if they're not comfortable with (or opposed to) it. The theory is that if companies start encrypting their content then open-source browsers will have to follow suit, but we already have that kind of junk; the difference is that now, with EME, we can keep 99% of the stack open standards, open-source, and auditable, rather than having to rely on Flash or Silverlight to do our decoding.
EME isn't the death of the open web, it's the death of the closed web. It's the death of awful, insecure, and obsolete technologies like Flash and Silverlight by taking the one single thing they're still good for and moving it to the browser. If EME failed and no one implemented it, Netflix wouldn't just stream their content unencrypted; they'd keep using Flash or Silverlight, or maybe implement something themselves so they didn't have to.