There's still a lot of disagreement over Passchendaele to this day, which is why you don't tend to hear much about it. The Brits especially don't like talking about it, and resisted admitting any culpability in the matter for years.

Case in point would be the mystery novel THE WOOD BEYOND by Reginald Hill. A good portion of the book deals with the lead character discovering what happened to his grandfather during the Battle of Passchendaele. However, when the BBC adapted it to screen, they cut all mention of Passchendaele out entirely and changed the WW1 subplot to something less controversial.