[geofft]

Yes, I think this argument applies to public sector unions as a whole. I think empirically, teachers' unions (and the postal worker's union, and so forth) have not been so, well, inclined to defend illegal and unconstitutional activity as police unions, so I'm not going to advocate as urgently for getting rid of them, but definitely they're also not quite like private sector unions for similar reasons.

(That said, both public schools and the post office have meaningful private-sector competitors, in the sense that the government can decide that they just don't need to fund so many teachers or postal workers anymore, and systems like vouchers for private schools make it look even more like a private-sector market.)