I was on /r/badhistory and I saw a post criticizing those who used Dan Carlin as a historical jumping-off point and talking about how his analysis of WWI is wrong. Why is this and why do some people not like him so much?
tl;dr: He's not a historian and says so himself. He's an entertainer. Many of the points he makes are historically inaccurate. It's an entertaining podcast, but not one you should be getting your facts from.
Really, this comment is the single best summary of why he's "controversial".
What is the post? Not trying to fan the flames here, but I can't find these supposed Carlin errors that everyone cites. I'm sure they exist (especially when you devote yourself to something as big as an entire world war), but surely all errors aren't equal.