Toland did not set up his fireteam to die. It was in his intentions to kill Crota, and he was fond of both Eris and Eriana. He did not intend in letting them die, he was just interested in Hive technology and using it for unknown purposes. They could be positive or negative. Osiris probably left of his own accord. The speaker sent Saint-14 soon after to retrieve Osiris, and he would not have done this if he is the one who made Osiris leave. Osiris simply was interested in using Vex technology for the purpose of the light and guardians, so his intentions were pure and clear. I don't necessarily think their is a difference between darkness and light. It is simply a matter of perception. If you think about it, the traveler abandoned the Eliksni as soon as the darkness touched them. This is obviously an act of cowardice, and the 'light' then caused the deaths of millions of beings. You cannot blame the Eliksni for wanting their property back, as we stole it from them and were not interested in sharing. Instead, we chose to massacre them. The Cabal. We think of them as bad, but really we provoked them. We invaded their base, their own territory. We hacked their computers, we stole their data. We killed their legions. And worst of all, we killed every leading cabal in our solar system. They were happy with just mars, but we had to massacre them. And they will strike back. I think that there is no difference between the light and darkness, and humanity must learn to use both of them in order to survive optimally. We will perish if we rely on the traveler, just as the Eliksni did.