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.
So, John, I like the analogy with the Ad Hitlerum (AH), but I do wonder if whether the fallaciousness of the two arguments (despite their formal similarity) is different. Here goes. The problem with AH is a relevance worry, namely, that even if the Nazis did X, it doesn’t follow that X is wrong (as there are, surely, many non-morally significant things Nazis did as Nazis). The problem with the Ad Regum (AR) is that it’s not clearly a worry about relevance, but more about speculation as to whether King would have done X. Of course, there could be a correlate relevance worry, but the AR is usually invoked to answer a question about issues of conscience and MLK is invoked as a form of argument from authority.
Scott, you make a good point. I think the two kinds of scheme could use more careful articulation than I’ve provided here. I think also there are variations on the AH and AR. For instance, sometimes the AH is a slippery slope style move (Hitler banned guns, and that was only the first step . . . ).
But I think what I was after yesterday was something like what you say in the middle. To put this differently, for all x, if MLK does (would do or would believe) x, then x is good; for all y, if Hitler does (would do or would believe) y then y is badness. In neither case is MLK or H a sufficient condition for goodness or badness. Both MLK and H are authorities of a kind (that’s why the AH works as it does), the question is whether their authority is relevant to a given case. More basically, people do the AR (as I’ve noticed) to show a kind of inconsistency. As the Daily Show segment pointed out, people generally invoke it to refute people they think must abide by every single view consistent with MLK. But MLK, your moral hero, would not support x, so therefore you’re inconsistent (or wrong).
As you point out, however, this could use more articulation.