[sageikosa]

"Having a union that endorses members will create a professional body that is superior to non-unioned workers" looks (to me) like an assertion that the value is in the union endorsement (and that it thus create the professional body), as opposed to the workers themselves.

As I've asserted, information workers are valued for their knowledge and problem solving skills, so unless this hypothetical union were going to certify people as having certain knowledge and problem solving skills and include/exclude members based on that certification (or give them a grading level), it will be meaningless as a value indicator to any employer. If I think the level they give me is too low, I won't be likely to stay associated with them. If employers think they rate people too high, they'll avoid them also.

If the "professional" union is just a middleman, I'd prefer not to have it, and I'm fairly certain sure employers wouldn't either.

Of course, professional bodies (outside of trade organizations) exist like this, but they are called consulting companies.