Hi,
https://forum.unity.com/threads/unity-and-macos-10-13-high-sierra.474527/
the problem is caused by the new APFS which is automatically installed on every High Sierra machine with an SSD.
You could try a workaround:
Create a new partition with the "Mac OS Extended" file system. After that just drag and drop your KSP installation into that partition und try to run the game.
I would try it myself but it seems to work fine on my machine ...