My point was that it is of course arguable that seeking higher wages and greater job security, etc. for one group of workers is inherently consistent with the public interest.  However, that argument is not the paramount consideration at the bargaining table.

I understand and appreciate Bruce's point, I just don't think we're addressing quite the same question. 

It's disturbing that labor unions lobbying government broadly on issues of worker pay, healthcare, time off and safe and clean conditions is considered equivalent to the narrow, private interests of, say, big pharma or the oil lobby.  And it's lame that public interest organizations like the Sierra Club are lumped in there, too.  I expect it from the Newt Gingriches.  His ilk have been hard at muddying those waters from the beginning.  But it's disheartening to hear it argued by folks from the left.

Sure, there are times, often in fact, when conflicts arise among different trades.  Working from the same book doesn't mean everyone's always on the same page.  And tensions between labor and environment are real, serious obstacles.  In fact, that tension could very well be the paramount wedge issue of these times.  The Gingriches sure as hell will continue to fan that flame.  But I don't think it's any coincidence that during rallies last winter in support of the events in Wisconsin, or during the WTO protests in Seattle, or at Occupy sites all over the world this past summer and fall labor and environment stood shoulder to shoulder.  What do folks imagine that solidarity represents if not to broadly serve the interests of everyone? 

I don't think General Electric and labor unions are up to the same thing at all when they lobby government in the context Destor offers:

 that these institutions can, in concert with the government, act to pass unpopular laws, start unpopular wars and let hedge fund managers pay a smaller percentage of their income in taxes than everyone else.

And I think I'm right to insist on a difference that isn't idiosyncratic.

By definition there can not be any particular group that qualifies as a public interest group, in that since it is a group, there is some defining characteristic which includes some of the public and excludes others.

There are those that will claim that they are working in the public interest - in fact most do - in that by achieving their legislative outcomes (and we are talking about control and influence on government here), there will be on balance a benefit to the public interest. 

Your comment above is an example of this:

Any gains made in the march toward democratic control of the Means of Production is a gain for all.  And while no collective bargaining deal is created equally, they are, by definition, in the public interest.

There will be others in this country, who are citizens and have as much equal say in this great democracy, that would disagree with you.  Some quite fervently and many of them will be ones who you believe to be beneficiaries of this march.  You can say that this folks are dupes or tools or deluded or corrupted. This may or may not be true.  But it is irrelevant to this discussion. The point here is what defines an action or intention as being in the public interest is a matter of perspective or viewpoint.

Any collective bargaining deal is not be definition in the public interest.  The right to engage in collective bargaining can be so defined (although some might argue that, too).  But the particular outcomes of those collective bargaining deals may or may not be in the public interest, depending on who you talk to.

 This is why it isn't splitting hairs to say that unions are not public interest groups, nor should all their actions be considered in the public interest by default.  Collective bargaining results that favor the workers or is beneficial to them are (from the liberal point of view) on the whole in the public interest, and as a result why the right to engage in it is so critical to health of the country and its democracy.

One can point to groups such clean water advocates who would argue there is no one who could argue that the public interest is not served by ensuring clean and drinkable water.  And of course no one could argue that it isn't.  But in the process of ensuring this outcome, the special interest advocates for clean water may propose regulations or require certain actions happen or not happen that one could argue is not in the public interest

See the debate over the pipeline in Nebraska - which some unions are not happy about the Obama administration nixing because an alternative route hasn't been finalized yet.  Would you side with the unions that want the pipeline to go through Nebraska's aquifer? Is that in the public interest?  That might be anecdotal but it goes to the core of the issue - Unions, like all special interests, have their agenda which seeks to benefit directly their constituency, which is going to at time run up against another group acting in the public interest.

So the koan today is: How can two public interest groups be in conflict if both are indeed operating in the interest of the public?

And this is where it comes back to what I originally put as the question at the center of the debate: what is the public interest?

You have your ideas about what constitute it, I have mine, Destor has his, Ironbolt has his, and there is going to be agreements and disagreements, and there will special interests groups that in each of our opinion are always acting in the public interest, others who never do (in spite of their claim that they are), and others who sometimes do and sometimes don't.  It is all a matter of debate.  Which makes it all sooo fun.