A particularly frequent subvariety of argument from authority is the, for lack of a better description, "even sophists find his arguments fallacious" scheme.  The thought is that even people likely to make bad arguments have special authority when they point out a bad argument.

I ran across an instance of this scheme on Balloon Juice.  Here's the whole post:

The National Catholic Reporter calls Obama the more pro-life candidate (via):

There is no doubt Obama is pro-choice. He has said so many times. There is also no doubt Romney is running on what he calls a pro-life platform. But any honest analysis of the facts shows the situation is much more complicated than that.
For example, Obama’s Affordable Care Act does not pay for abortions. In Massachusetts, Romney’s health care law does. Obama favors, and included in the Affordable Care Act, $250 million of support for vulnerable pregnant women and alternatives to abortion. This support will make abortions much less likely, since most abortions are economic. Romney, on the other hand, has endorsed Wisconsin Republican Paul Ryan’s budget, which will cut hundreds of millions of dollars out of the federal plans that support poor women. The undoubted effect: The number of abortions in the United States will increase. On these facts, Obama is much more pro-life than Romney.

That’s some good reasoning, but it’s preceded by a defense of Cardinal Dolan that includes Canon Law justification of Dolan paying pedophile priests. In a way, that makes it even more remarkable, since even someone who can defend Dolan for that kind of stuff sees through the Romney/Ryan bullshit.

The last part is the key.  There is indeed something strangely compelling about that kind of reasoning.  But I think on logical grounds this fails miserably.  First, I'm not sure I see bad arguments increasing a person's authority.  Second, it's oddly selective; i.e., usually such a person has no authority, but here that they have come to the conclusion I find palatable I find them convincing.  But perhaps on this occasion their reasoning is also flawed.  My sense then is that this sort of scheme undermines rather than strengthens someone's authority. 

In fairness to mistermix, the author of the post, his primary point is that the reasoning in the cited passage was indeed good.  To that extent my comment here is tangential.  It's just that this reasoning was seen to be given more probabitive force by instances of reasoning poorly (earlier in the article).

Interested in comments on this one.