Meritocracy is a dogwhistle white supremacists created to justify their position of power over people of color.

No.
“American Dream,” was built on belief where workplaces are meritocratic environments where workers, regardless of their background, can, on merit and abilities overcome any deprived situation they may find themselves in and rise above.

Just like communism when the Wall fell, I think it's safe to say this ideology, when tried and tested, has been proven a total and complete failure.

No.

Currently: "meritocracy" has nothing to do with "merit" and more to do with eugenics, it's just a word to make white-supremacist-patriarchal-cis-heteronormative-abled-supremacist bigotry sound less terrible than it is.

In general: because hierarchy is bad for society, since someone always ends up at the artificial "bottom" and treated badly or at the very least as less worthy or deserving (of life, dignity, freedom, access, and so on). The only reason anyone would want/believe in a "meritocracy" is because it makes them feel superior to others.