They don't sacrifice their souls, they kill each other physically because by worshiping the darkness they are allowed to grow stronger with each killing blow (part of the sword logic) their souls are protected deep in their throne worlds. When you say we summoned crota, technically its his nature to find and kill civilizations especially ones helped by the traveler, same with Oryx and Savathun. So as soon as we partnered with the traveler we pretty much permanently moved up on the hives kill list. If you're saying we performed a ritual purposefully or accidentally we definitively need more [b]specific[/b] info before we can say that is a viable theory