It’s a lie told by unions to preserve their position as the arbiter of salaries. Remove the lie and their role becomes extremely diminished.
But come on, do you really contend that you have no means to measure if one teacher is better than another? That teachers are the one job out there where it’s impossible to determine who does a good job and who does a bad job?
It’s amazing you seem to advocate against this… it’s an opportunity for you to earn more.