[Jim Noble]

If this is constitutional, then so is a state law that prohibits its electors from casting electoral votes for women or black people

Not the same thing.

All state laws which bind the freedom of Electors are unconstitutional. So, a law prohibiting Electors (once appointed) from voting for a woman or a black person would be unconstitutional.

But it would NOT be unconstitutional for Louisiana (say) to appoint David Duke as an elector, knowing that he would not vote for a black person.

[Alberta's Child]

Are you suggesting that a state could pass a law prohibiting black people from appearing on the ballot?