Understanding the argument -
Sociologist: Widespread acceptance of the idea that individuals are incapable of looking after their own welfare is injurious to a democracy. - Premise. How is it injurious to democracy? The basic premise of democracy is that people know what's best for them, and they act accordingly. They vote. But if people don't even know what's best for them or they can't make their personal decisions, the basic thread of democracy breaks.
So, legislators who value democracy should not propose any law prohibiting behavior that is not harmful to anyone besides the person engaging in it. - Conclusion. Example - If someone doesn't take the proper diet or someone is not taking proper sunlight to get the required vitamin D (bad for a person but may not necessarily be bad for the entire country. Probably as a country, there are more important issues to handle than ensuring right decisions for every person in the country), the conclusion is that, say, the Supreme Court should not make laws prohibiting the person from eating a bad diet/not taking proper sunlight. Making such laws for everything would mean that legislators don't believe people can take care of themselves.
The conclusion is that lawmakers should not make laws (managing people's personal lives or views) that project as if people cannot make decisions themselves.
After all, the assumptions (people can or can't make their decisions) that appear to guide legislators will often become widely accepted. - supporting premise for the conclusion, just like the 1st premise. What happens if that becomes widely accepted? Then, it's not good for democracy.
The sociologist’s argument requires the assumption that
Option Elimination - We must find the missing premise, minimum condition, or assumption.
(A) democratically elected legislators invariably have favorable attitudes toward the preservation of democracy - out of scope.
(B) people tend to believe what is believed by those who are prominent and powerful - The scope of the argument is to find a missing premise for the conclusion: "So legislators who value democracy should not propose any law prohibiting behavior." Let's see if we add this
Premise 1- Widespread acceptance of idea X is injurious to democracy.
Premise 2- Legislators' assumptions will become widely accepted.
Added premise - people tend to believe what is believed by those who are prominent and powerful
Conclusion - So, legislators should not propose any law prohibiting behavior.
This statement has no bearing on the conclusion and is out of scope.
(C) legislators often seem to be guided by the assumption that individuals are incapable of looking after their own welfare, even though these legislators also seem to value democracy -
Premise 1- Widespread acceptance of idea X is injurious to democracy.
Premise 2- Legislators' assumptions will become widely accepted.
Added premise - legislators often seem to be guided by the assumption that individuals are incapable of looking after their own welfare.
Conclusion - So, legislators should not propose any law prohibiting behavior.
It's as if we are saying that X often seems to be guided by the assumption that people are incapable of taking care of themselves. So, X should not propose laws that project people incapable of taking care of themselves. Distortion.
(D) in most cases, behavior that is harmful to the person who engages in it is harmful to no one else - out of scope.
(E) a legislator proposing a law prohibiting an act that can harm only the person performing the act will seem to be assuming that individuals are incapable of looking after their own welfare.
Premise 1- Widespread acceptance of idea X is injurious to democracy.
Premise 2- Legislators' assumptions will become widely accepted.
Added premise - a legislator proposing a law prohibiting an act that can harm only the person performing the act will seem to be assuming that individuals are incapable of looking after their own welfare.
Conclusion - So, legislators should not propose any law prohibiting behavior. Why? Because Premise 2, and as Premise 1 says, it's injurious to democracy. Ok.