You have the argumentum ad Hiterlum, whereby any proposition p consistent with Hitler’s beliefs b or actions a is ipso facto wrong. Now you have the ad regem (still working on the name), where any proposition p consistent with the beliefs b or actions a of Martin Luther King, Jr. is ipso facto correct.
By way of Think Progress, and last night’s Daily Show, we have an example:
WARD: I think Martin Luther King, Jr. would agree with me if he were alive today that if African Americans had been given the right to keep and bear arms from day one of the country’s founding, perhaps slavery might not have been a chapter in our history.
This obviously suffers from terminal factual problems, but so powerful is the thought of Martin Luther King, Jr. that no one bothers to check what he believed any more. He’s good, therefore he supports any view that’s good. Hitler is bad, therefore he supports any view that’s bad, like gun control (which he didn’t support, actually). But thus the fallacy.