But aren't all jobs essentially "merit" based? If you are a bad factory worker, you get fired. If you suck at flipping burgers at Burger King, you get fired. The idea that you can't fire a teacher because her students aren't learning is absurd.
The problem is that there is no objective way of measuring a teacher's ability, whereas it's very easy to tell if someone "sucks at flipping burgers".
Exactamundo, Franzl.
A personal anecdote, FWIW: My mother was a suburban school teacher for close to 30 years, and a registered Republican for as long (though admittedly she voted for Obama and Dukakis). Her take on merit pay is that it was doled out primarily to those who were the principal's or superentendint's drinking buddies more than on "merit".