So, with any semantic question like this one, there are several ways we can go. One is to sling around dictionary definitions and sociological concepts and run around in circles arguing about what a word really means (answer: at bottom nothing. It has no inherent meaning, it's just a referent.)
Or, we can do something a little differently, and try to dig down and figure out the real question we're asking. When there's a semantic argument like this, I've found that it's most often because we're arguing about some totally different underlying question, using word definitions as a proxy for that argument.
There are several possibilities for the underlying question here, and I suspect different people are angling after different questions. Here are a few possibilities:
-can an individual white person ever be the subject of negative behavior from an individual due to their race? (obviously yes)
-can an individual white person ever be the subject of negative behavior from an institution, or an individual representing an institution, due to their race? (again, obviously yes)
-do white people in general have an equivalent level of experiences where they're disadvantaged due to race, whether by individuals or institutions, as black people? (obviously not)
-is it possible for specific individual white people to have experiences with racism that are equal to or worse than individual black people? (again, yes--the bell curves overlap at some point)
Now, of course, because this we're humans and we have feelings and whatnot, there are several other entangled things we might be trying to do:
-express annoyance at other people belittling or mocking things that have happened to us
-express annoyance at our group being attacked, which feels just like an attack against us personally, when we personally have done nothing wrong
-signal our political team
-probably a bunch of other stuff, I dunno, I don't know everything.
Or, since this thread was a response to a specific post in another thread, we might really be arguing about one of these questions:
-in a thread where members are sharing stories of racism they've experienced, is it ok and appropriate for white people to also share stories? (well, that depends. Are you wanting to share your story in answer to the thread's question, or because you are uncomfortable with the fact that minorities experience a whole lot more racism more often and want to try to balance things out in the thread? In the former case, go ahead, in the latter, come on dude.)
-in a thread where members are sharing stories of racism they've experienced, is it ok for some members to tell others that their stories aren't really racism? (well, I'd think really hard before doing it. It's not cool to belittle other people's problems and experiences that way, even when they are orders of magnitude less bad than your own or someone else's. This, for the record, is why I think "first world problems" is a bullshit meme that needs to die. Oh, and this also applies to people trying to explain away people's stories with "well, but maybe it wasn't really racism but xyz was happening!" Yeah, maybe. But how many "well, but maybes" do you need to go through before you figure out that no, really, it's fucking racism?)
Anyway. I think it's generally useful in this sort of argument to take a moment, and pause, and ask yourself what question you're really trying to answer. And if maybe, possibly, other people who you think are being stubborn asshole jerks might be trying to answer a different question.
If a tree falls in the forest and no one's around, does it make a sound? I dunno, depends on what question you're really asking!