Which is fine now, but what happens when Windows 9 and DX12 drop in 2015, and all the new features and APIs only work with Metro UI apps? Suddenly all those desktop applications are second class citizens. By Windows 10 or so, non-Metro apps will be slower, heavier, and crippled relative to Metro apps, and it'll be hard to even find modern and supported tools to develop and compile them. And that's assuming Microsoft doesn't make deliberately crippling moves - throwing up warnings about "uncertified and potentially dangerous" applications or blocking uncertified desktop applications from using some features (webcam, arbitrary ports, whatever) without configuration changes.
The reason people are speaking up now is not out of fear of Windows 8, but out of fear of Windows 9 or 10.
Fun Fact: Desktop applications can use Metro APIs. Chrome is a good example of this. Upon installing Chrome on a Windows 8 computer, you can use it through the metro interface.
The reason people are speaking up now is not out of fear of Windows 8, but out of fear of Windows 9 or 10.