There is no proof SFF needs any conversation of the sort. Innuendos about a "narrow set of authors" without documentation or any sort or definition of what "narrow" means in the first place are just that, innuendos. There is also no "compared to what?" If SFF needs this conversation then so does women's romance novels, the NBA, rap music and Indian cricket. Surprise - the politically correct have no interest in that, and the reason is obvious. This is not being offended by a neutral principle everyone can benefit from. This is specifically and only targeting anything too white, too male, and too heterosexual because it's an auto-KKK. Everything else gets a pass. The PC do the same with history - there is only ever British or European colonialism. Mughals, Aztecs, Incans, Arabs, Ottomans and Mameluks all disappear in their complaints, as if by magic. There has never been institutional white or male supremacy in SFF. The idea is as ridiculous as race, sex, gay = interesting literature.1) That there are no conversations about biases in other fields does not invalidate discussions about such things in sf/f. This assumes nobody is having those conversations, but I gather you, like me, are not an expert in Indian cricket or romance novels, or the NBA, or rap music (though, I'll accept that you might be an expert in one of those). This means the point is irrelevant. At best, it's a faulty comparison fallacy.
There's also the assumption here that fans of sf/f who are critical of its representation of people are obligated to talk about representation issues in other fields. This would be like telling the Financial Times it is now obligated to cover Seattle Seahawks games or Nature to cover horse racing or a Congressman to represent the interests of people in another state. These things may be connected on some sort of common ground, but they are not contextually relevant to the declared interests of each thing. At best, this is absurd.
2) Context matters for what we discuss. People talk about European slavery in the West because it is the most relevant, immediate history of slavery *for the West.* Whether Aztecs had slaves isn't relevant to the immediate history of slavery here, nor to the structural racism that followed the end of the slave trade in Europe and, eventually, in the United States. This applies to colonialism as well. If we were discussing a cultural context in which another form of colonialism or slavery were relevant, it would certainly be important to acknowledge such things.
Indeed, even within discussions of U.S. slavery (and colonialism), there are long debates and discussions about, for example, black people buying and trading other black people as slaves (a fact which makes sense only if you put it in the context of the slave trade in the U.S., which was primarily run by and in service to white people -- crazy, I know). These topics *are* discussed regularly in academic circles, but considering that most Americans couldn't tell you much about a random African, Middle Eastern, or, hell, even European country (except, perhaps, random stereotypes (not necessarily negative ones) and little tidbits of info), this seems a moot point. I can no more control what people don't know than you can. Yeah, all those other places (as far as I know) had slavery. Did the Aztecs have slaves during colonial times in America? No. So why would a conversation about slavery in America or England need to discuss these other issues? You seem to have a problem with the fact that people aren't raising irrelevant issues in specific cultural contexts where that would be bizarre at best. If you want to hear about Aztec slavery, there are books on tlacotins.
3) Your claim that diversity arguments are exclusively an attack on white, heterosexual males is not quite a straw man, but close enough that I'll call it one. Considering that there are women who have been criticized for their positions on various things (Elizabeth Moon and Sarah Hoyt, for example -- not necessarily on the same scale) and plenty of folks who are white, hetero males have been part of the call for diversity, I can easily conclude that your statement is nonsense.
Next, the argument that there has never been an institution of white supremacy in sf/f is laughable. Considering what Samuel R. Delany says here, and the fact that publishing in general was in fact structurally racist throughout much of the 20th century (earlier too, but that's obvious), any claim to the effect that sf/f has not been affected by racism or white supremacy (this is the wrong term, but given your loose use for it, I'll let it slide) is woefully ignorant of actual history. One would have to have read a lot about the Harlem Renaissance and learned about decades of sf/f history, and then one would have to pretend all of that never happened. That's the only way this claim works. Blind, willful ignorance (or, technically, just ignorance).
4) Just because you don't find certain kinds of literature interesting does not mean others do not. I don't much care for a lot of things, but I'm happy to recognize that a lot of people do like those things. Good for them.
5) This whole thing is about you playing victim, not because you're actually a victim, but because being one is convenient for your "cause." And that's sad.
And that's probably all I'll ever say about this individual. Laters.