If terrorists are attacking your citizens across an international border and the government of the country in which the terrorists have their bases have indicated that they have no control over that area, that it is essentially lawless, then isn't the government of that country under attack entirely justified in taking military action to wipe out the threat?
I say it is.
Since the job of government is to protect the life and liberty of its citizens, I say they are perfectly justified. In fact, only if Ankara doesn't move against the terrorists of the PKK will it be deserving of approbation. Those in Iraq who object most strongly to Turkish action should have been in the forefront of those demanding that action be taken by the Iraqi government. In the name of protecting its own citizens, the failure leaves Turkey with no choice.
As always, the threat of serious military action is itself often sufficient to bring peace and relative sanity. Let us hope that it does so in this case.