Prove it. Sources and or links please.
======================
I don't down about Horowitz but I can give you a couple of very good sources: Prescot's "The Conquest of Peru" and "The Conquest of Mexico". Neither book is a quick read, both books have lots of fine print, and lots and lots of pages, and next to zero illustrations. (And yes, I have read them both.)
And, remember, just because something is bad doesn't mean it's wrong.
Some obvious parallels to the American invasion of Iraq (except that the Americans and British troops did most of the heavy lifting in 2003). The Aztecs were every bit as nasty to their subjects as the Baathists were to theirs.