You yourself told the parent "many experts disagree with your assessment", when the parent clearly indicated that they simply were following what appears to be the academic consensus on this book, today.
The link I provided has a clear link to further work you can go explore, and make up your own mind. But I sort of suspect that in the three cases of 1) the parent comment, 2) the wikipedia article, and 3) now this statement about the American conquest, you have already decided what you want to believe.
I'm not personally an expert in this field. So I am not going to go and update the wikipedia article. What I am going to do, is to listen to the people who are experts in the field. I actually loved Diamond's book when it first came out, but over many years, I have not found a single academic historian who had good things to say about it. And it's not for lack of trying. As much as the book has received many awards, it is today simply a fact that it has a very fraught reputation in academic circles.