It is quite easy to understand the Turkish caution on the Kurds.
Prior to the Gulf War of 1991 Kurds attacked Turkish soldiers and institutions.
After 1991, hundreds of thousands of Kurds sought sanctuary in Turkey from Sadam Hussein.
From 1991 until recently, Kurds attacked Turkish soldiers and institutions.
Now, hundreds of thousands of Kurds have sought sanctuary in Turkey from IS.
If/When IS is defeated, will Kurds start attacking Turkish soldiers and institutions again?
I don’t know, but I’d certainly be cautious about arming them.