The author in this model essay never answers or presents counterarguments to his many rhetorical questions. So why would the author choose to conclude a paragraph and write this essay in the form of questions? By allowing, inviting, and 'opening up' to counterarguments, counterclaims, and rebuttals, don't questions weaken or worsen an argumentative essay?
In asking a question in this manner, the author uses (or tries to use!) rhetorical questions. The author does not expect a response - indeed, such a response is not possible, because the responder has way to insert himself or herself into the piece. These questions are not meant for "allowing, inviting, and 'opening up' to counterarguments." It appears the author's intent is to ask questions that (to the author) have obvious answers in a way to engage the reader more.
Rather than looking at an artificial, bad example, it would be more helpful to look at a canonical good example: the speech given by the Corcyrean Envoy at Sparta prior as told by Thucydides. In the opening of the speech, the envoy effectively makes use of several rhetorical questions.
In the piece you're referring to, I see four questions. The two in the first paragraph aren't rhetorical questions. The second question there is a clarification of the first, and the first is setting up an ostensibly stronger claim than the claim to be proved, on the idea that if you prove the stronger claim, you thereby prove the weaker claim as well. It's not a rhetorical question because the writer proceeds to attempt to answer the question. Similarly with the question in the third paragraph: the writer raises this question as a possible objection to the argument he's presenting, and proceeds to answer the question to rebut that possible objection. The question at the end of the second paragraph is the only rhetorical question in the piece. Rhetorical questions are questions that are not intended to be answered (and that the writer doesn't proceed to try to answer). They pose a question with a seemingly obvious answer in order to use that implied answer as a step in their argument. They can be effective argumentative tactics in persuasive writing in general, but I always discouraged them when teaching philosophical writing because the gold-standard of clarity in an argument is having all the premises of an argument stated explicitly. Dan Dennett advises to always try answering rhetorical questions (similar to his advice to always have a "ding" go off in your mind when you come across the words "of course," "obviously," etc. in an argument), to guard against arguments sneaking in unquestioned assumptions.