There are a bunch of reasons why strict membership would be problematic.
First is the level of informal training that forms the basis for a lot of (good and bad) software developer's knowledge/ability. Certification favors some approved educational requirements. Second is the fact that professional certification is at its strongest when membership/non membership is a pretty decent indicator of competence. IE a certified plumber will instal toilets that consistently flush downward. Will a certified software developer be more likely to improve a client's chances that a project will be delivered and solve the problem its trying to solve?
That said, I can't see a strong objection to a voluntary organization recruiting members and seeing if they can add some value somewhere. Hopefully they don't try to keep all the compilers to themselves.
Realtors certify through a moral test rather than a professional one. The test is simply a way to define a minimum standard, and a way to expel immoral incompetents.
Realtors established a code of ethics, and made one of the articles in the code to be competent and knowledgeable, and if incapable of a job to turn it down or refer it to someone who can do it. They enforce this with precedents establishing minimal expectations, which are as precedents are flexible as times change.
If your organization actively enforced a 'Programmer code of ethics', and programmers were facing expulsion for being fuckups, I think that's "likely to improve a client's chances that a project will be delivered and solve the problem its trying to solve."
The ultimate problem is that expulsion has to be a real punishment. You can do that through changing laws to make membership actually not voluntary, though it may still be nominally voluntary (like doctors, and lawyers), or to distribute resources for work through the organization (like realtors), or to simply refuse to work with organizations that use people who don't belong to the organization (like actors and stagecraft unions, for example) and to be large enough for that to make a difference.
First is the level of informal training that forms the basis for a lot of (good and bad) software developer's knowledge/ability. Certification favors some approved educational requirements. Second is the fact that professional certification is at its strongest when membership/non membership is a pretty decent indicator of competence. IE a certified plumber will instal toilets that consistently flush downward. Will a certified software developer be more likely to improve a client's chances that a project will be delivered and solve the problem its trying to solve?
That said, I can't see a strong objection to a voluntary organization recruiting members and seeing if they can add some value somewhere. Hopefully they don't try to keep all the compilers to themselves.