There are other reasons, such as goading them into a pointless destructive war to begin with… but I gave my example, which is her sending the fleets to be destroyed by Azshara. You said this could be a case of necessary sacrifice, but I don’t see how and stated why I think it’s a stupid move here:
She is intentionally weakening the Horde while simultaneously pushing them into a second war with Azshara on top of the one they are fighting with the Alliance. How is this a good example of a necessary sacrifice? You then said “pick another example”… but that does me no good, because we aren’t talking about whether “sacrifices” can be necessary or not; we are talking about a specific example… in which case the sacrifice doesn’t seem to be doing the Horde any good at all. Therefor I add it to the list of reasons why I think Sylvanas is betraying the Horde and everything it stands for.