This is a question about the story. Why do you think orcs get so many second chances when we never give those to any other race? Why do we need orcs to be at full strength to fight the legion? I am asking this because this is the most common excuse. !We need to be together at all costs or the legion will win! We never give this reasoning to all the other races that alliance and horde attack and destroy, we don't try to unite with them. We don't think about legion's coming when we invade and steal their lands. We kill them all for even smaller offences. We don't mostly try to look for goodness in these 'evil' races,but orcs are all forgiven because of thrall and some few.
And that is why i think that Siege of Orgrimmar should be presented as a blow to orcish aggressive mentality and remind them they are not always be gonna be tolerated and they are not irreplaceable. They should see their ideals crushed. Not just heroic rebels saving the city from a tyrant.