It is understandable though JS96.
The 'aleague' excluded the other clubs on national identity grounds.
If a person hits another person you cannot expect the victim to just accept it. The striker may not have a problem and be friendly after but it is a lot harder for the victim to simply ignore it and move on.
I can see why the reactions are there at the same time as hoping the rift will heal in time.
As I think Grazor said somewhere - once the rift is healed the antagonism becomes outright and relevant sporting rivalry. Having former NSL teams included in the same competition as aleague teams (like in the Australia Cup) would add a fantastic level of competition to the fixtures.
It would have a feeling like the old days of Roar v Gold Coast, with the 'superstar, pedestal boys' of the Gold Coast holding a particular place of 'sport hatred' in our orange hearts.