There is a difference between a military sniper who protects the troops by killing those who would harm them and some guy who was out to kill one individual they disagreed with politically.
Most people would call James Earl Ray a murderer for assassinating MLK. Ray was not fighting in a war to protect American interest from terrorism. He was convicted of his first crime, a burglary in California, in 1949. In 1952 he served two years for armed robbery of a taxi driver in Illinois. In 1955, he was convicted of mail fraud after stealing money orders.
Ray was sentenced to twenty years in prison for repeated offenses. He escaped from the Missouri State Penitentiary in 1967 before he assassinated MLK on April 4, 1968.
Chris Kyle was decorated U.S. Navy SEAL whose sole mission was to protect his comrades. James Earl Ray is no Chris Kyle!