Would you care to elaborate on what you mean here?

Whites are a majority. So aggression from them toward a minority like Asians would be "punching down".

Immigrants are typically a minority, so if they were discriminating or being aggressive towards the majority then it'd be considered "punching up".

So what about black american on immigrant discrimination?

Regular punching I suppose. Regardless all punching is bad. It's just that there is some nuance in how it's dealt with. Much like big kids punching much smaller kids (and vice versa) on the playground.

This reduces to making discrimination and prejudice acceptable for certain groups.

A better analogy would be the smaller kid finding yet another, even smaller kid to beat down.

Then avoiding any mention of the smaller bully, because they were being bullied by someone larger. Nothing positive or nuanced about this position.