As a population, on average, teachers simply aren't that impressive. Teaching is a noble vocation and ought to have great status. But when the average teacher simply isn't that good, people aren't going to extend much respect to the profession.
And the unions contribute to that condition by resisting efforts to improve the quality of the teacher population.
To extend that to the teaching population is madness. Where are you determing "the average teacher simply isn't that good"? How are you making that conclusion? Because it sounds like you just pulled it out of thin air, or it's just a personal view you have.
To say that teachers don't deserve a higher status because "some [imaginative] proportion" are "simply not good [according to you]" is laughable.
The reality is that many of the schools, and many of the teachers, are just bad. This can't be acknowledged in the public debate, so it isn't addressed. The unions have established a structure dedicated to protecting bad and mediocre teachers. Which is why great teachers can't get paid appropriately -- the unions would never allow it. It's also why teachers don't enjoy higher status: As a group, they really don't deserve it.
Yes, the unions are right that, without tenure and their workplace rules, teacher hiring and pay would be a political game. That's what political systems do, they respond to political incentives. That's the whole idea of charters: to move the accountability of the schools out of the political system and into the hands of a constituency invested in actual quality. It's probably true that _today_ parents as a group aren't completely equipped to handle that role, because they've been trained to just send their kids off to school. But as they get the opportunity to make more decisions and influence the schools' offerings, they'll come up to speed.
tldr; The testing apparatus is a symptom of a broken governance apparatus. The solution is to fix the governance and incentives. So long as the incentives are political, the results will be political.