The PKK is a far more complex issue. Their mission is self-determination for Kurdish people. After WWI, the Allied powers split the region where the Kurds reside, their hoped-for Kurdistan, between Turkey, Iraq, and Syria. They have faced oppression and worse (e.g., Iraq murdered Kurdish civilians with chemical weapons in the 1980s) from these governments for generations.
In Iraq: In the contest with Saddam Hussein, at least beginning in the 1990s, the U.S. built a strong relationship with the Kurds there. The Kurds used U.S. support to create de facto autonomy from the Iraqi government (something they are voting on in a couple of weeks - potentially a major event in Kurdish history). They became a skilled combat force and strong allies of the U.S., fighting alongside the Americans through the Iraq War and now in the fight against ISIL.
In Syria: My impression is that the relationship between the U.S. and the Iraqi Kurds extends now, with the Syrian civil war, to the Kurds in Syria. Like those in Iraq, the Syrian Kurds also have used their government's weakness to establish some autonomy.
In Turkey: There is no government weakness and no autonomy, but an ongoing contest with crackdowns, terrorist attacks, and more. The Turkish government calls the PKK 'terrorists', but the government's hands are hardly clean. The Turkish government does not want autonomous Kurdish regions in Syria and Iraq, both of which would border the Kurdish region in Turkey and would encourage and support Turkish Kurds.
Are the PKK terrorists? Freedom fighters? Some of each? I can't tell you. But certainly they have some argument for seeking self-determination in the face of oppression, and unlike groups such as ISIL their goal is self-determination for their own people, not to bring down governments and to take land and liberty from others.