Okay. So I designated some time to read over the Cabal lore again. The Cabal joining in the Light vs Darkness was because we kept attacking them along side with the Vex on Mars. The events of the Taken War and the constant bombardment on their leaders and fleets made them desperate. The highest of the Cabal in our Solar System sent word to Ghaul about the Dreadnaught and he told them to try to take it. Failing to do so and being taken himself, the rest of the Cabal were losing in their fights against the enemy races and sent a distress signal to the Ghaul. I think a reason for why I still think the cabal are kind of irrelevant (aside from the Psions that are messing with time) is Ghaul was the reason the militarized like that. Out of the Cabal that have been named by Calus, not too many of them are even alive. You have Calus' daughter and a few others. (Not to say there aren't others out there.) I feel as though if they were to stay involved, then It would be time to either scrap the existing cabal enemies (psions, legions, colossi etc.) and bring out the other races that have been ingrained into their society. Or have them join the light in the battle against the Darkness, since that seems to be a constant fear of theirs. Destiny only has 4 more years left until the end. So I'm curious to see what will happen to the Cabal empire.

I meant even before Mars. Unlike the fallen who followed the traveler or the hive who followed the darkness, the Cabal just stumbled upon us.