No, by attacking one of the major groups involved in the fight against ISIS, Turkey has made ISIS stronger. At a time when PKK is most willing to cooperate with the Turkish government, Turkey has only expanded on it's campaign against the PKK instead of focusing on the real threat of ISIS.
Turkey was not justified in killing 70 suspected members of the KWP because it put the lives of civilians in danger without cause. There is never an appropriate time to send the military in to a civilian-populated area and put the lives of innocent people at risk, no matter what the offending party has done.
There is absolutely no way anyone can actually go ahead and justify a country killing as many people as they did. Yes, they were suspected people of that party that could have ended very badly, but I don't think that all of those people deserved to die. What if they weren't actually members of that party and they were innocent? Killing people to prevent killing doesn't make it right.
Turkey was not justified in killing seventy suspected members of the Kurdistan Workers Party in a bid to prevent chaos in its cities. Governments should not execute their people unless if they have been convicted of a specific crime. Turkey's killing of seventy people only suspected to be part of the Kurdistan Workers Party demonstrates a lack of a fair justic system.