Besides what you say is not considered a valid argument... "Many people in the field say..."

Not considered by whom? You? In what way is it 'invalid' to point out that most experts and scientists disagree with his arguments?

I understand that anthropologists are very sensitive towards everything that is considered western imperialism but calling something bullshit only because it refrains from criticizing past conquerors is careless.

Did you read the criticisms that were posted? It's not about sensitivity, its the fact that most of the evidence and arguments that Diamond makes are just factually wrong. The vast majority of what he argues is not backed up by anything, and some of it is directly refuted by actual science.

It becomes about sensitivity only when you read into some of the questionable conclusions that are drawn from his cherrypicking of facts and baseless hypotheses.

To quote an actual scientist writing in an actual scientific journal:

[Diamond] claims to produce reliable, scientific answers to these problems when in fact he does not have such answers, and he resolutely ignores the findings of social science while advancing old and discredited theories of environmental determinism.

Why does pop science have a bad reputation? Because you can write pretty much anything you like without having to have evidence for your claims, and there is no one to hold you to account.

I admit, Diamond is relatively harmless, but it is examples like this that breed the culture that leads to situations where the opinions of actual experts and scientists are given the same level of respect and consideration as laymen who don't believe in vaccines or global warming.