LSAT Question Explanation
PT 108, Section 2, Question 21
Parallel FlawArgument structure
Genetically engineered plants will be harmful.
Some experts say that genetically engineered plants will not be a problem. Those same experts claimed in the past that introducing non-native plants would be fine, but now it's clear that non-native plants are a serious problem.
Explanation
This argument claims that genetically engineered plants will be harmful because the experts who say they're safe were wrong about something else in the past.
This is an ad hominem flaw. These experts may not have a perfect track record, but this is not a logical reason to claim that genetically engineered plants will definitely be harmful.
Answer choices
This argument is flawed, but in a different way than the stimulus. It relies on some people's complaints which are contradictory in nature (these people want lower taxes and more government services...). Then it makes a completely unsupported conclusion. But it doesn't say that some people were wrong in the past therefore they'll be wrong again, which is what happened in the stimulus.
This argument is flawed because the author says the last film was great, so the next one will be too. Past results can't perfectly predict the future. But this is a different flaw than the stimulus. Note that the critics in this answer choice were correct in the past, in the stimulus the experts were wrong in the past.
This is the same flaw as the stimulus. The author here says that some economists were wrong in the past, therefore they'll be wrong again about the current economic expansion.
This is a better argument than the stimulus, although it's still not great. Maybe if parents buy traditional toys they won't go out of style and the children won't beg and plead for trendy toys. Or maybe children just beg for trendy toys no matter what, who knows. But there's no ad hominem flaw here saying someone was wrong in the past so they'll be wrong again.
This is concluding that if experts predictions come true then it won't be because of the predictions, which is different from the stimulus. The evidence given looks tempting because it says that the experts were wrong in the past, but the conclusion doesn't match the stimulus which said some experts will be wrong again.