To the Editor: Leon Klinghoffer, our father, was one innocent civilian among thousands who were murdered under the rule of Yasir Arafat and the P.L.O. As a family who has unfortunately been touched by Mr. Arafat's terrorism, we find that our only solace in his death is that he cannot kill anyone ever again. It is mind-boggling that some would view him as a diplomat, martyr, hero and even a peacemaker. This is definitely not how we know him to be. To us, Mr. Arafat will always be a murderer and a terrorist; and one less terrorist on this earth...