The root issue is making inequality of outcome the issue rather than inequality of opportunity.

The alarmists lose if you argue the front end rather than the output.

You can effectively manage opportunity, you cannot manage the output.

Invent a time machine, go back to the 1920's, shoot all the cultural Marxists.

I think part of it is to deflate the underlying argument. Those making the argument are mixing up cause, effect, and conveyance. Perhaps one inroad is to demonstrate that there is no underlying reason why people of different cultures, races, nationalities have the same interests - that the existence of a difference is not itself a harm to anyone.

Essentially the argument is talking about a "spherical cow", rather than a real one. I believe, and personal experience drives this, that people who realize the argument is about numbers and not real people view the argument very differently - they realize it is an argument without merit.

So perhaps there is your answer. You win the moral argument by illustrating "they" aren't talking about real people and show how real people are harmed by their so-called solutions.