Sin’as Chinam does not mean “baseless hatred”.
It means “pointless hatred”.
My point is about holding grudges, even if the hatred initially had cause, perhaps even started out with a halachically appropriate one.
Should you still hold on to the hatred, because it has a basis, even though it serves no purpose?
I am arguing that it is still sin’as chinam, and still an expression of the sin that cost us the Second Commonwealth and its Temple.