Comment by MarkusQ

It would be even harder to read if the author didn't do that.

We are being invited to consider a premise (i.e. presume that it is true) and explore the consequences. At any point, we can choose to disagree with this premise, but at least we understand it.

Imagine instead if the author, after inviting us to accept the premise, proceeded to write as if we were to assume the premise were false. It would be much harder to understand what they were proposing or why they even wrote the piece in the first place. At best it would be a maze of obligatory qualifiers and nested hypotheticals.