Adam, I see a serious problem in these three quotes:
As i see it, though, answer B is really just a "who cares?" answer choice. Who cares if the people in the painting looked like some actual people from history, whether living or dead, famous or not? Why would that make us doubt the conclusion that the artist who later became well known painted the painting when he was younger and just starting out?
and:
In my view, answer B raises no doubts at all. I would completely shrug it off. Don't try to rationalize why it could hurt the argument. Just ask yourself "does this make me worry about the conclusion?"
and:
I'll also weigh in on the somewhat passionate earlier discussion about answer C by saying that it, too, gives me no pause. I read it and said to myself "so what, who cares?" Okay, fine, artists use live models. What does that have to do with whether the artist painted the painting that includes a person that looks a lot like him? It gives me no reason to question the conclusion. It's a nothing burger.
In all of them, you evaluate answer choices in terms of whether they weaken the
conclusion. But that's not what we've been asked to find. What we've been asked to find is an answer choice that weakens the
argument, a very different task indeed. After all, just because an answer choice weakens the support relation between the premises and the conclusion (thereby making us worry about whether the argument is any good), that doesn't mean it weakens the conclusion at all or gives us any reason whatsoever to doubt that the conclusion is true. Lousy arguments are given for true conclusions all the time.
This matters because now we have no reason to reject (B) or (C). Sure, they give us no reason to doubt the
conclusion, but so what? They might still undermine the alleged support provided by the premises for the conclusion, in which case they would be correct.
I think the premises can be (somewhat generously) simplified into this premise: one of the figures depicted as an aristocrat in the anonymous painting is a painter who lived when it was painted. From this, the argument concludes that this painter is the one who painted the anonymous painting. We're tasked with finding an answer choice that gives us a reason to worry about the inference from the premise to the conclusion, i.e. to think, "even if that premise is true, it turns out it doesn't really give us much reason to accept that conclusion."
I can see why (B) fails to weaken the argument. All it suggests is that the figure in question is (like the majority of the depicted figures) a real person from history. That has no tendency to undermine the inference from "that figure was a contemporaneous painter" to "he painted the painting". On the contrary, what would weaken the argument is if the figure depicted
weren't a real person from history. The only way I can see (B) weakening the argument is if "from history" is (mis)interpreted to mean "from long before the painting was painted": that would suggest that the close resemblance should be discounted, thereby taking away our reason for thinking the figure depicted is the painter of the self-portrait.
(C) draws our attention to an alternative possibility in which the premise is true and the conclusion false: perhaps the contemporaneous painter was merely a model for someone else's painting. This is an alternative possibility that might have occurred to anyone reading the original argument. Unfortunately, (C) doesn't do anything to make that possibility more likely than it already was prior to reading the answer choices. It merely states that the practice in question was "not uncommon", and so we've learned virtually nothing about whether this painting did or did not involve the use of live models for the depicted figures. But even if (C) had told us outright that this painting definitely involved the use of live models, it's not clear whether that would weaken the argument, simply because it's not clear how common it was for a painter to use himself as a live model. If we knew that self-modeling was in fact rare and that the figures depicted were all live models, then I think
that would weaken the argument. But (C) fails to do so as it stands.
But I don't think (D) weakens the argument either. Not merely because violations of etiquette are
possible, but because violations of etiquette are
rampant. If we're trying to figure out whether someone performed a certain act, learning that it would count as a violation of etiquette tells us nothing about whether they did it, unless we already know that the agent in question is scrupulous about etiquette and/or that the violation would be likely to be discovered. What do we know about this individual? Well, he's an artist, and of course artists are notorious for flying in the face of convention and even deliberately seeking to shock 'squares' and 'normals'. If anything, then, it's less likely than usual that etiquette matters to this individual. Would this violation be likely to be discovered? We have no idea. A battle scene presumably contains many figures, and we don't know how prominent the figure in question is. Nor do we know how recognizable or obscure a figure the artist was in society. Nor do we know whether the painting was even intended for public showing. In the end, then, we have no reason whatsoever to deem it unlikely that the artist committed this violation of etiquette, which means (D) fails to weaken the argument.
As for (E), there's nothing unlikely about an artist painting a battle that took place in the distant past. And I don't think anyone has suggested (A) is a good answer.
My conclusion is that this is a poorly composed LSAT question.