Well, so far we didn‘t get any of their perspective, just guess work re: their motivations on the part of everyone else. I also hope that black oil creature isn‘t supposed to be what the Ba‘ul look like in their natural state, because that would be a lazy entry into the „the bad species is the dark colored, ugly one“ annals. (Not to mention that the last sentient oil slick was the one which got Tasha Yar...)