You obviously feel that it's useless, which is debatableIf you want to bring it up again, this time I'll throw Teach For America onto the list of organizations that say it has no impact.[1]
that it's a professional barrier to entry which requires extra time or money to get
This is exactly credentialism. EXACTLY. "I don't know if it provides any benefit, but it takes time and money to get" is the perfect description for a useless credentialism structure.
when you know that means “nights and weekends at no extra pay”
I really don't know this. NPR seems to be part of the conspiracy keeping me ignorant [2]. Teachers work about 30 or so minutes less per day than other professionals, and that includes weekend work.
How would you feel if your CEO kept talking about your company is releasing buggy code and we need to hire better programmers and make shipping bug-free code a key part of your pay?
Like any professional, I would leave and get a different job. Fortunately my profession has not worked hard to arrange that there is only one employer in town. Since my wages are roughly what I would get on the market, as opposed to being set by some third party despite my market value, it means I haven't priced myself out of other jobs. My current employer pays me (roughly) enough to keep me around which is (roughly) what I would get elsewhere.
If I was being paid way above market for some reason, though, I'd raise a stink to high heaven and keep a hold of that prior job no matter what.
Modulo the need to keep things staffed for a whole semester, switching jobs into or out of teaching should not be as insanely difficult as it is. The beneficiaries of this system are the high-seniority people currently in the field who have no plans to leave. If someone wants to switch into teaching from another career, they need to go through the silly Masters-In-Ed hoops via night school. If someone wants to switch out after a few years, they are walking away with nothing from their pension-vesting system, and they have a "Masters In Education" degree which no one values besides school boards that have negotiated contracts.
[1] http://www.theatlantic.com/magazine/archive/2010/01/what-mak...
[2] http://stateimpact.npr.org/ohio/2011/10/05/teachers-work-few...