What it comes down to is that Angel honestly believes that he has the right to make decisions affecting the lives of others without getting their permission or even informing them of what has happened. If any other member of the cast were to try the same thing, there would never be any doubt that what they were doing was wrong and would lead to at the very least, personal heartbreak and disaster. Willow, Giles, and Wes have all, at one time or another been guilty of this. But we must never lose track of one very important and undeniable truth: the name of the show is "Angel," which means that he can do pretty much whatever he wants to, whenever he pleases, and there will always be some "Get Out Of Jail Free" clause that will make anything that he does right and an act of heroic self sacrifice.
In other words, he may not always be right, but he will always be the star of the show, and the star of the show can never be wrong. Makes perfect sense if you look at it that way.