Hi LSAT2018!
This tough question, like most every Flaw question, boils down to the exact phrasing (and logical force implied) by the conclusion.
It's true that many of those who dispute the fact that Shakespeare (who, with apologies to Will Smith, was the original 'Big Willie Style'
) actually authored his plays were descendants of those aristocrats proposed as potentially the true authors of the works. However, the conclusion doesn't discard their opinions merely because of their potentially personal connections to the issue of who was the true author.
Instead, the author jumps to an unreasonable amount of power when they concluded that these claims were motivated
purely by snobbery.
Providing some idea that there may be snobbery involved (being that these claims come from the descendants of aristocrats who likely would have looked down at someone who was merely the son of a glove maker) is not sufficient to conclude that the apparent snobbery was the
only motivation behind their position. The original aristocrats may very well have been elitist snobs and their descendants in question could also very well be the most awful, stereotypical trust-fund jerks, but they also may be correct in their reasoning that Shakespeare was not the true author.
The question is similar to one that states that since doctors have a motivation to dislike some herbal supplement that could negatively affect the doctor's business, the doctors' claims about the dangers of the supplements are
purely due to selfish motivations. True, the doctors to have a personal reason to advocate against the use of these particular supplements, but they also could be doing so because the supplements are legitimately dangerous to one's health.
This argument would have functioned as a Source Argument fallacy had the argument concluded along the lines of: The claims by these doctors about the danger of these supplements should be disregarded, because the doctors have a selfish motivation in wanting to keep these remedies unavailable for purchase.
In the Shakespeare stimulus in question, a Source Argument would have read like: Pay no mind to the claims made in doubt of Shakespeare's true authorship of these works, since the objections are coming from descendants of the aristocrats who could otherwise be argued to be the true authors.
Due to the use of the exclusive language with the word
purely in the conclusion, this question falls more under a category of an unsupported amount of logical force rather than a classic Source Argument.
Hope that was helpful!