Not all evil is just about personal gain. That's way oversimplified. Sure, some is and that can be part of it, but sometimes it isn't.

Bhaal is the lord of murder, and not usually doing it to gain anything. "Bhaal only lived to hunt and kill, the presence of the living instilling in him an overpowering desire for death and destruction. He was at all times a cruel, violent and hateful being, though his behavior could vary from cold and calculating ruthlessness to a savage thirst for blood."

Evil is basically desire to do harm or to have power over others (which I'd argue is the same thing). Tyranny is evil because it removes others ability to do what they want, which is harmful. It's about a desire. A desire to have power over someone, or to harm someone, or to kill someone, etc. Gaining power over someone isn't the disregard for consequences, it is regarding them and choosing tyranny.

However, good actions also often do this. You kill bad people, imprison criminals, etc. It's good because you were trying to help/protect someone. Not good would be anything else, which both neutral and evil have to fit in there somewhere. Neutral must be without regard, and evil must be with regard and intent to do the opposite. If not, what is neutral or evil if it's not those?