Do not talk down towards other fans for liking things in different degrees than other people. It stops now.
Further, if you take the statement "white people as the problem" as being equivalent to someones saying "black people being the problem" you are missing the point. The context of the statement is that "representation is the problem."
If you equate the statements, you're fundamentally misunderstanding the argument. Unless you feel that black people are far too frequently used at the expense of other people, the statements are not analogous. The "problem" is that people feel that minorities aren't shown enough. Given that I'm a white man, I can recognize this and not take offense if someone happens to frame it as "too many white people is a problem" instead of "not enough minorities is the problem" since both things are effectively asking for the same thing.
Attempts to silence and derail the discussions will not be tolerated. This is a warning.
Advocating the inclusion of something is inherently different than advocating the exclusion of its counter-part.
There's no middle ground. You just don't celebrate that a certain demographic is missing for some misguided reason. This is like when people say "I'm so tired of straight white male protagonists omg". Sure their (justified) intention is that they want something else, but their message being conveyed is that straight white males aren't welcome. It's hypocritical.
I'm not North American but I've been to the USA and I've noticed that political correctness is generally skewed towards accepting inclusion more than exclusion. If the OP was phrased in such a way that it only celebrates the inclusion of diverse demographics then I wouldn't give it a second look. On the contrary I'm always up for diversity. I'm a Lebanese Middle Eastern Mediterranean dark-skinned gay man. I belong in the "diversity" bunch. I advocate for it.
Of course the discussion can and should continue normally without someone trying to shut it down as you said. I just wish the OP was phrased better.
As it stands now, it doesn't sit right with me.