Many Natives also deny it but it's undeniable.
There's plenty of archeological evidence and more modern taboos in the culture that indicate that cannibalism was once normalized.
If you talk to non-politicized elders, they confirm the downfall of the Anasazi was brutal, as was the territorial expansion of my ancestors - the Na-Dene bands - into traditionally Pueblo lands.
Pueblo usually call Navajo, Utes, Apaches "enemies" or "killers" in Native language.
Yep considering the fact that the fall of the pueblo city states occurred some 500+ years ago yet still exists in the oral tradition of practically every SW tribe speaks to the brutality of the event.
Also I think that some elders might not want to talk about the event because it might challenge the legitimacy of some of their reservation land claims. IIRC correctly the Apache and some other tribe have been at it over land claims regarding this event