How do the Prophets reconcile the truth about humanity with the war they are waging? Do they even truly believe?

In particular, I would love to hear some interpretations from the Halo 3 era, before 343 decided to go all in on Forerunners as a weird separate vampire-looking species. Presumably the Prophet of Truth knows that he is killing his own gods. Does any of the lore of the 2007 era franchise explore this?