But Sirhan Sirhan has not seen the outside of a jail since, what, 1968? I think the message is clear; If you are going to shoot someone, shoot a conservative.
Hinckley was acquitted. Not guilty. The only appropriate question is whether he's "cured," whether or not he is a danger to himself or others.
Making punishment, retribution, deterrence or politics considerations in mental health evaluations is an incredibly dangerous path to start down. The Soviets, among many others, used mental illness as a proxy for punishing antisocial or criminal behavior (however defined), which perverted both justice and psychiatry.
Agca, on the other hand, was convicted in a court of law. Punishment, retribution and deterrence are perfectly appropriate considerations in his sentence.