I did not intend to imply that historians were writing racist explanations for why Europe was able to colonize most of the world - sorry if that is how it came across! Instead, I believe those views were common among mainstream society. Part of that is because there had not been a cohesive, insightful, and popular alternate explanation.

McNeill is indeed one of the few historians who were investigating this question - and unfortunately I haven't read any of his work. However, I don't think that Jared Diamond was just repeating McNeill's argument because the back of my copy of Guns, Germs, and Steel has this excerpt from a review that McNeill gave the book:

There is nothing like a radically new angle of vision for bringing out unsuspected dimensions of a subject, and that is what Jared Diamond has done.

I dug up the full review online here. There's certainly lots of criticism in the review - particularly of that epilogue. But also pay attention to how much McNeill praises Diamond for the new ideas he brings forward.

What he has to say about developments in South-east Asia and the islands of the southwest Pacific was nothing short of a revelation.

Diamond’s account of why relatively few herd animals can be successfully domesticated was news to me.

Diamond’s observation that some of the major fertile regions of Eurasia lie at approximately the same latitude, so that crops can travel east and west without having to adjust to seasonal differences in day-lengths, was also an eye-opener for me. ... By contrast, the spread of maize from its heartland in Central America was hindered by the fact that its growth pattern, linked to changing day-lengths, had to wait many centuries for random genetic variation to produce plants adapted to different latitudes.

By emphasizing climatic and geographical obstacles to the diffusion of crops and other useful innovations within the Americas and Africa, he brings out an important dimension of the past which I had never considered before.

Once again, much of what Diamond has to say in these chapters was entirely new to me. I was not previously aware, for example, that archaeological investigation in the uplands of New Guinea seems to show that inhabitants of those secluded valleys resorted to food production not very long after the earliest known development of agriculture in the Middle East.

Diamond’s account of how speakers of Austronesian languages expanded their domain across enormous distances was also a surprise ... Linguistic affinities and archaeology provide the basis for this reconstruction of one of the most far-ranging human migrations of all time. I had never before understood how its separate episodes combine into a single pattern.

The tone of this review is radically different from those reddit threads. The modern online discourse about Diamond has amplified all of the criticisms from early reviews like McNeill's, but entirely removed all of the praise. One of the reddit threads compared Diamond to a student faking a chemistry experiment - I certainly don't think that McNeill had the same perspective! McNeill seems to have an honest disagreement with Diamond, he doesn't think that he's a fraud.

Reading those reddit threads can definitely make someone develop a heuristic "to not believe any analysis that Diamond presents, since there's a significant probability that it's misleading". But I think that's a shame, because Diamond has lots of unique, well-praised insights that are missing from the discussion in those threads.

Ah yes, that comparison makes sense.

The prologue to Guns, Germs, and Steel outlines what Diamond sees as the most common explanations for the differences between peoples, and then uses the rest of the book to show why they are wrong and to offer a different explanation.

Probably the commonest explanation involves implicitly or explicitly assuming biological differences among peoples. In the centuries after A.D. 1500, as European explorers became aware of the wide differences among the world's peoples in technology and political organization, they assumed that those differences arose from differences in innate ability. With the rise of Darwinian theory, explanations were recast in terms of natural selection and of evolutionary descent. 

Today, segments of Western society publicly repudiate racism. Yet many (perhaps most!) Westerners continue to accept racist explanations privately or subconsciously. In Japan and many other countries, such explanations are still advanced publicly and without apology. 

These explanations are still somewhat common today, and I believe that they were much more common in 1997 when the book was published. Even in the comments section on this post there is a suggestion that the Tasmanians' technological regression was caused by biology - a population bottleneck causing inbreeding (I'm not saying that argument is the same as the 'Darwinian' one, just that it is also an explanation stemming from biological differences). 

Guns, Germs, and Steel kicked off a genre of discussion that attempted to explain why Europe took over the world without assuming biological superiority. It seems like at the time, Diamond was explaining something new.

Devereaux’s quote there is similar to the argument that Diamond puts forward in the epilogue of his book. Diamond argues that the geography of Europe, with lots of mountains and peninsulas, encouraged the formation of lots of smaller countries, while the geography of China encouraged one large empire. So while one emperor could end Zheng He’s voyages, Europe’s geography encouraged the countries to compete and experiment. Columbus was Italian after all, but had to go to the competing kingdom of Spain to fund his voyage.

I agree that that is a harder question! Diamond doesn’t devote a ton of space to it however, the book focuses on Eurasia compared to the Americas/Africa/Oceania, and not really on Europe vs other parts of Eurasia.

My point in bringing it up is not so say necessarily that Diamond is correct, it’s just that if you read Diamond’s critics you might think that half of the book is about Pizarro and half is about Zheng He - when it’s actually mostly about things like the types of grass that cows eat.

I’m just trying to show that we can trust Diamond not to cherry-pick evidence when writing this article about Tasmania.

Thank you for bringing this up - I'm sure that many people have seen those arguments and rate Diamond lower because of them. I have read each of those reddit posts over the years and have disagreements with them, I do not believe that, in it’s entirety, Diamond’s work is characterized by cherry-picking.

I find that arguments against Guns, Germs and Steel tend to be specifically about two chapters of the book, and also knock Diamond for pushing a monocausual explanation instead of a multicausual one.

The first chapter that's most commonly criticized is the epilogue - where Diamond puts forth a potential argument for why Europe, and not China, was the major colonial power.  This argument is not central to the thesis of the book in any way, and Diamond warns the reader that he's speculating in this chapter, so I'm more than willing to look past it. I'm happy to see that none of the threads you linked to contain this line of attack, but it's a common one I see online.

The other chapter that's often the subject of attack is "Collision at Cajamarca" and focuses on Pizzaro's conquest of the Incans.  Again, I don't think it's fair to reduce a 400+ page book down to a single chapter. The main issue here is that Diamond seems to take Pizzaro's account at face value - which I can accept as a valid criticism, but Diamond's critics take this too far.  These arguments downplay how important disease was to Pizzaro's victory - and in some cases completely deny that Pizzaro and the Spanish won decisively. I see in those posts things like "The European conquest was hardly decisive" and "conquest was never a cut and dry issue", citing later rebellions against Spanish rule.  While it's true that there were Indian revolts against the Spanish over the remaining centuries, the basic fact is that today they mostly speak Spanish in Peru and they don't speak Quechua in Spain. I don't think we can point to a few Indian revolts and claim that civilizations in Eurasia did not have an easier time conquering the New World than vice versa.

The final common argument is that Diamond focuses too much on "geographical determinism" and should instead find a variety of causes. I disagree with that line of thinking for the reasons outlined here.

Why would the die rolls keep favouring this one place? (And you can't invoke the law of large numbers. There are only five continents in the world, and modern economic growth did not have to happen anywhere at all.)

To get from Europe 1 AD to modernity, while paying reasonable attention to the many accidents along the way, there are really only two possible narrative genres.

The first is the rock falling down a mountain. It starts with one big, random event. This then triggers other events, and they trigger others, and now you have an unstoppable landslide. But the chance is at the start.

The second is the cyclist pushing his bike up a mountain. It takes an actor who deliberately over time overcomes one obstacle and dodges another, until eventually they get to the top, and from there it's a downhill ride.

Diamond's approach is of the "rock falling down a mountain" genre. It's much more likely that one big factor favored Eurasia, rather than lots of little things just happened to go their way time and time again. One of the few good arguments against Guns, Germs and Steel that I've seen is from LessWrong, and actually argues that in some places Diamond tries to find multiple factors, when in reality there are probably fewer!

In my mind a big portion of this hostility from historians comes from the fact that Diamond is himself, not an historian, and the historians aren't happy that one of the most famous history books of the past thirty years came from someone outside of their field. You can see this hostility in some of those reddit posts. I don't think it's right to dismiss all of their arguments because of this, but I want to point out that they are not unbiased observers.

I would also like to link to this significantly more detailed defense of Guns, Germs and Steel. It does a much better job defending Diamond than I can here.