it would be a problem if they aged quickly, but they are a long-lived race. In all that time they can find a thousand ways to cure their addiction
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Ignorance does not exempt them from their actions. They are addicted, it is a fact; and even after knowing it, they want to remain addicted and drain the lives of other living beings to satiate their addiction.
Of course, after the sunwell restoration they stopped draining lives, but I am sure that if sunwell had not been restored, they would continue draining lives.
The weight of their morals is not in doing the logical thing to save some lives, it is in choosing to satisfy their addiction through the dispossession of the vital force of other living beings (it doesn't matter if they were non-sapient). If they exclusively did it to save the children and the old ones, it could be justifiable.The blood elves had to stave off a crippling - and at times deadly - addiction whilst also fighting an impossible war that threatened the end of their entire species. I think draining a few non-sapient creatures of their mana to deal with the addiction whilst dragging their society back from the brink is perfectly justifiable.
like exile? you have to understand that an immigrant does not have a good time in his first moments, and if you add their ailments... it is something less pleasant.The high elves away from Quel'Thalas, like Vereesa, had the luxury of dealing with their pangs in much safer environments.