No arguing with this one since he thinks Arthas was bad from the start. No he was a noble man with an anger streak and got pushed to the point of questionable. After Frostmourne he pretty much turned villain.
I was thinking the same thing
Except Illidan forcing fate by bringing Argus to us would help beat the Legion for good. What Sylvanas seems to want is break the veil between life and Death with screws with the natural order of things. There's a bit of a difference. Life and Death went on before the Legion came about and it will after. This mental gymnastics with Sylvanas is absurd.