What Diamond glosses over is that just because you have guns and steel does not mean you should use them for colonial and imperial purposes. Or handing out smallpox-infested blankets from sick wards.Which, in a post calling itself 'Real History vs. Guns, Germs, and Steel' is a bit much.
How do you think smallpox entered the Americas?
No idea? It wasn't intentionally thrust upon the native population (although I'm sure if they'd known of its effects, the conquistadors would have done so). In 1513, smallpox was introduced by a single Spaniard to the new colony at Buenos Aires. It was this smallpox that led to the death of Wayna Qhapaq, Sapa Inka of Tawantinsuyu, by, from the Spanish perspective, fortuitous accident. This smallpox precipitated a succession squabble and civil war between Waskar and Atawallpa that further weakened the empire. In 1520, smallpox was introduced to Mexico, again accidentally, by a soldier sent by the governor of Cuba to hunt down Cortes, who had disobeyed his orders (none of the conquistadors were particularly well-organised, although Cortes had a knack for negotiation and politicking). It was this epidemic that killed a bulk of the Mexican population, allowing its easy domination by the Europeans. Both of these epidemics were accidental.
And again, the 'environmental/geographical determinism' trope rears its ugly head. G,G,&S isn't a work of environmental determinism. Not even close. It doesn't say, 'Geography forced Cortes to kill Aztecs'. It says, to paraphrase, 'Geography made it easy for Cortes to kill Aztecs'. There's an enormous difference there, and anthropologists are keen to ignore it. They accuse Diamond of lacking nuance and of ploughing on with his rigid and idiotic environmental determinism - and when he goes and writes another book, Collapse, that foregrounds the topic of human actions in the 'collapse' of societies, they accuse him of changing tack. Are they really so lacking in imagination and insight that they don't see these books as two sides of the same coin?
Agency isn't magic, and it really doesn't explain anything. It's just a black box anthropologists use to avoid having to come up with causal explanations, and you are unlikely to find a naturalistic explanation of it. It's just like free will - they say it isn't, but of course it is. It's just a continuation of the Christian concept, and it's just as spooky. If time were spent engaging with the philosophical literature on action - Donald Davidson, etc - then we might be getting somewhere, but agency is just a way to allow anthropologists to avoid causation (which they don't like, because studying causation would make anthropology, well, scientific). And all the agency in the world is worth nothing without means. G,G,&S is fundamentally about the means. The motives are, after all, much more obvious.
Despite Diamond releasing a book which foregrounds human agency, so-called, in explaining human phenomena, the anthropologists like to believe that he advocates for environmental determinism. They see the latter book as a change of heart, instead of thinking that maybe their straw man wasn't quite accurate. It's disappointing to see such bad thinking coming from professional thinkers. It seems, yet again, to be motivated by the fact that Diamond isn't from within the confines of academic anthropology and hasn't drunk the continental Kool Aid.
One day, I hope, anthropologists will cease to be so tribal. I don't see that happening soon, though.