I've finished the prologue of Guns, Germs, and Steel, and want to write down a few brief thoughts.
Firstly, Diamond makes a considerable effort to assure his readers that he's not a eurocentrist. I can understand why he feels the need to do this, but from my perspective it just made him come across as a smug progressive.
It's perhaps worth noting that my general affect for Professor Diamond has been mostly negative, due to his reputation as, shall we say, a skeptic of civilization. For someone like me, with allergies, asthma, nearsightedness and an ideological affinity for modern world, that sort of mindset rubs me the wrong way.
I'm reading this book, not out of a genuine desire to fairly evaluate the works of people I disagree with, but because it was recommended. Not to me personally, but in general, by educational YouTuber C.G.P. Grey. In a pair of videos, Grey presented Diamond's hypothesis from the book, which sufficiently piqued my interest for me to suspend my suspicions and pick up a copy from the local used book store.
Getting back to the book itself--I think the prologue dismisses several alternative hypotheses out of hand. Now I'm not a professional geographer, so maybe there's a strong body of evidence that those hypotheses are indeed wrong, and Diamond's explanations are intended for convincing a lay audience, rather than a contrarian such as myself. Since in all likelihood the truth is an amalgamation of these possible causes, I'm willing to overlook these seemingly weak arguments.
Certainly I haven't been dissuaded from reading onward. The first chapter is clearly written and informative. My advice would be rather for a certain sort of reader to skip most of the prologue and its disclaimers, heading directly for the meat of the book.