They're going to protect their border by slaughtering Kurds. I hope if they cross into Syria they get crushed by Russia. Turkey has been supporting ISIS all along and has only bombed Kurds. To hell with them! Literally!
Well, I take a more U.S. position than you. I hope that the Kurds prevail against the Turks. But if Turkey and Russia go at it, I hope they crush each other, or Russia gets crushed.
Russia is not fighting ISIS, by the way, they are only fighting the rebels who are against Iran's pet Assad. They don't care about ISIS or saving Christians.
But geopolitics is real, and a vast part of Syria is a no man's land causing chaos. I certainly wouldn't want Turkey tell the U.S. we can't defend our border, so I couldn't in all honsety say it's illegitmate for Turkey to defend their border. And going into former Syrian territory could be a legitimate necessity for that.
But all of this is moot, since Turkey and Russia will not go to wat. They both have to much economically to lose. They are still allies, even if there is tension right now. Russia despearately needs to sell them oil, and Turkey needs that oil.