It sounds like you're saying it's fine to be racist against whites, but offensive to do the same thing to your personal "in-group." Little ironic, lol.
Often, when people are referring to racism, they're referring specifically to Institutional racism. As a general rule (because everything is naturally full of gray areas) it's considered to be impossible for whites to experience institutional racism in countries where we're the majority. So while a PoC could certainly be bigoted against whites, it wouldn't be accurate to say that they're inflicting institutional racism on them.
Institutional racism is defined (according to the wikipedia article you link to) as unequal statistical outcomes and unequal statistical treatment (e.g. group X being more likely to live in poor neighborhoods), sliced by race.
White people can certainly experience this in countries where they are the majority. As an example taken directly from the wikipedia article, white people significantly underperform Asians on standardized tests, they are more likely to live in poor neighborhoods, have worse health, and are disproportionately likely to be "targeted" by police (also they commit less crime).
Can you cite any piece of evidence in favor of institutional racism by whites against blacks that doesn't also support institutional racism by asians against whites?
" As a general rule (because everything is naturally full of gray areas) it's considered to be impossible for whites to experience institutional racism in countries where we're the majority."
Sorry, what? Considered by whom? Because we should have a word with these people about how unimaginative they are.
For one thing, there are plenty of ways a member of group X could experience institutional racism in an X-majority country. Perhaps they live in a Y-dominated region of the country, or work for a Y-owned company, or group Y has more political/economic/cultural power in society despite being a minority, or they work for an organization whose policy is to hire and promote Y preferentially.
More generally, I don't see the purpose of desperately insisting that institutional racism can never affect group X. To say that group X can be harmed certainly doesn't mean that group Y isn't harmed more. It's a weird and pointless linguistic game that harms the purpose of achieving equality of opportunity by gratuitously driving away allies.
I know it's lazy to just link to a Wikipedia article on the subject, but I'm going to anyway, because I'm too lazy to address all the things in your post when you can do your own research.
The fact is, the occasional inconvenience on whites in America (as a convenient example) from occasional pockets of bigoted blacks is fundamentally different from the regular impact on blacks from the institutionalized racist tendencies in society.
He thinks I'm racist for quoting wikipedia. I've met people like him at work. Overly sensitive people is exactly why I don't want to write about race issues.