But percentages are zero sum. You can't increase diversity without decreasing homogeneity.

Increasing a minority will require decreasing the share of the majority. Either you're okay with that or you're not.

I'm not sure I follow. If a company has 75% from group A and 25% from group B while these groups make up 66% and 33% of the population respectively then it makes sense to address the underrepresentation of group B. But why would we applaud a 50/50 ratio? Isn't that just an underrepresentation if group A? A majority is not necessarily an overrepresentation.

This line if thing seems liable to give credence to the notion that "diversity" is a dog whistle for achieving an underrepresentation of undesirable groups (men, Whites, and increasingly Asians).

Then by definition you are not "all for diversity".

Depends. In my view you can be all for diversity but at the same time not deliberately attempt to achieve an underrepresentation of a particular group.

It reminds me of mercantilism.