Tenure dying in NYC

Today's report in the New York Times shows a categorical shift in New York City public schools: nearly half of the teachers up for tenure last year were denied it.
Again, just so we're all defining our terms, tenure gives one due process before firing; it does not guarantee a job.
The reason that it was so hard-fought for originally (and remains what is dismissed as a "sacred cow" in the article) is education is a profession particularly vulnerable to abuse of power, and, should your administrator not like your politics, your personal choices, or, indeed, the fact that you keep insisting on speaking up on behalf of your students, well, how very easy it is to give you a bad review and get rid of you.
Given the amount of pressure that's come from upper levels of NYCPS, it isn't surprising that the principals have caved. It was Mayor Bloomberg, after all, who said that he'd "end tenure as we know it." The article indicates that there have been very heavy amounts of guidance from central administration on their teacher reviews this year. Principals have to, by virtue of their position, be keenly aware of political and policy shifts; their numbers had to look different this year.
And of course NYC is using those notoriously changeable value-added scores as one-third of their decisions, which means it's a decent bet that at least half of those teachers would have gotten a different result next year.
This is a good way to end up with a profession of people who no longer speak up, certainly. Do we really want that in our schools?