This one: http://www.markshuttleworth.com/archives/1295

    Mir is really important work. When lots of competitors
    attack a project on purely political grounds, you have 
    to wonder what THEIR agenda is. At least we know now who 
    belongs to the Open Source Tea Party   And to put all 
    the hue and cry into context: Mir is relevant for 
    approximately 1% of all developers, just those who think 
    about shell development. Every app developer will 
    consume Mir through their toolkit. By contrast, those 
    same outraged individuals have NIH’d just about every 
    important piece of the stack they can get their hands 
    on… most notably SystemD, which is hugely invasive and 
    hardly justified. What closely to see how competitors to 
    Canonical torture the English language in their efforts 
    to justify how those toolkits should support Windows but 
    not Mir. But we’ll get it done, and it will be amazing.

In context, this was written shortly after Martin Gräßlin had said that he would not support Mir in KWin. KWin is the KDE window manager/shell; he is one of those "1% of all developers" for whom the display server really matters. And unlike what Mark claims, KWin does not support Windows (other parts of the Qt and KDE stack do, but not KWin).

So, he sees this as his time essentially being volunteered for him by Mark, to support a display server with an architecture he doesn't agree with, after he's already put the effort in to support the display server that pretty much everyone else in the desktop Linux ecosystem have been targeting. And if you don't agree with Mark, or the technical decisions made leading to Mir, you get branded as "the Open Source Tea Party", "purely political", an "outraged individual" who has "NIH'd just about every piece of the stack."