I'm not a history expert, but I think non-voluntary guild might be an oxymoron, and that stopping non-guild members from practicing the craft was part of what a guild did.
One of the reasons why calling it a Guild rather than a Union is that Union has a lot of negative connotations in a lot of countries (here in the UK for example the Unions have a bad reputation for been difficult to work with and older people remember their role in the late 70's).
Also Union has connotations of "Union Shop" which is definitely something that a lot of people regard as negative.
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I'm thinking more of an organisation that exists to protect programmers, represent our interests publicly, has internal standards and recommendations as par for the course, I doubt the old master/apprentice relationship would translate or for that matter the journeymen systems.
Here in the UK we have the British Computer Society which (theoretically) does something similar but in practice I'm not really sure that they actually do (and as an aside the two people I did know who had paid to join I wouldn't have employed to sweep up).
I'm not sure how well it would work out though since it strikes me as something with a high degree of cat herding built in :).
"here in the UK for example the Unions have a bad reputation for been difficult to work with and older people remember their role in the late 70's"
Of course, that depends on your political persuasion: a lot of us have sympathy for the union workers who were brutally crushed by Thatcher's government in the 80's. Speaking as a programmer who has been a union member in a previous job, I would be supportive of a programmer's union.
Without rehashing the old arguments Thatcher's destruction of the Unions would have been far harder to achieve had they not ground the entire economy to a halt frequently in the late 70's, I'm neither left or right wing in my politics (as much as possible since those labels are crude and inaccurate at best) but the blame is as much the Union's as Thatcher's in this instance.
I personally think that Union's on the whole are probably a good thing (something has to exist to balance the power of capital) but that the UK model was fundamentally broken (I actually like the German model.
... and a Guild doesn't have negative connotations?
Is this a cultural thing? Because for me (west coast of Canada, in my 30's), the only connotation that comes with the term "Guild" is a historical protectionist organization that ensures only those in the Guild are allowed to practice that craft, membership is non-voluntary. It carries a connotation of extreme corruption as well.
Am I just not exposed to the modern usage of the term?