NYC Tenure Cont'd

NYC Educator disagrees with my take on the NYC tenure debate, and a previous post in which I cited his recitation of the many transcendently bad teachers with which he's had the misfortune to work as evidence that the tenure process in New York should be improved. 

For the most part, I like NYC Educator's take on things; it's a good blog and he's correct in saying that he "specifically told [me] that the city has been negligent in enforcing existing tenure rules for over thirty years." I should have noted that in the previous post. 

However, even his assertion of past negligence is true--and it may be--I'm not sure why it's an argument against the new proposed tenure policy. If the administration has neglected to enforce tenure in the past, why is it bad that they're trying to do so now? NYC Educator thinks they don't need value-added to weed out the bad teachers; the administration obviously thinks they'd be better off with the additional student performance data. Why are they wrong? I'm having a hard time figuring out what the administration's agenda here could be, if not to deny tenure to teachers who shouldn't get it.