Critic: Political utility determines the popularity of a metaphor.
Conclusion (therefore)
The society-as-body-governed-by-a-head metaphor promotes greater acceptance of authoritarian repression than do other metaphors (such as society-as-family).
Evidence
Political utility determines metaphor popularity. The body-with-head metaphor is pervasive in authoritarian societies.
Evaluate
The first two sentences give us premises with an overlapping idea of "popularity / prevalence". We can synthesize those two claims to get the idea that
in authoritarian societies, the metaphor of society as a human body has a lot of political utility.
That's what the premises establish: this metaphor has a lot of political utility for authoritarians.
The author takes it from there to the idea that, .
We don't know anything about other metaphors. Are they also pervasive in authoritarian societies? Do they also have political utility? The author is Assuming a Difference, thinking that the Body metaphor is more pervasive /useful than the other metaphors.
Even if we grant that the Body metaphor is the most useful metaphor, does its usefulness have to be "promoting acceptance of repression"?
Couldn't there be other things that are politically useful to an authoritarian government? Maybe the Body metaphor encourages different components of society to work more nicely with each other.
Goal
Let's look for an answer saying that the Body metaphor is useful for some reason unrelated to "getting the people to accept repression", or for an answer making it seem like one of the other metaphors could be just as pervasive / useful.