I agree with your statement but feel that environmental determinism cannot be brushed off. Surely geography as well as culture accounts for the current supremacy of the "west". It can be argued that Indo-European culture originated (along with language) in the region of present day Georgia. Vast areas are wasteland and tribalism and disfunctional Islamism dominate the greater perportion of the Indo-European territory. Disease and lack of resources surely are influential.
The fact that someone is liberal doesn't mean they are totally wrong. Rather it alerts the reader to look for intentional and unintentional bias. Bias in presentation does not, by itself, void the basic concept.
He does present a number of problems for consideration. One can reasonably disagree whether the solutions he offers solves them but there's no denying we face a number of threats. Burying our heads like the proverbial ostrich in the sand will not make them go away. Of course Diamond is a liberal. His politics leave something to be desired but he still shows us things its good to want to learn about.
I agree. As I posted earlier, parts of his book are interesting but his underlying thesis is deeply flawed. He is but another sprig from a long line of academic anti- western civilization doom and gloomers.