@FultonHoover because 1 is not enough so it is implied that 2 or more is necessary. It does not mean that 2 is enough to do it, but it will take at least 2, since 1 is insufficient.

@MelanieLorraineTrevino I read it as a conclusion because the choice is there to have the operation, or to alternatively not have the operation (the argument for the author then becomes "Should I have the operation?". I try to rephrase things like that and it has helped me a lot, phrasing parts of the passage into easier digested questions. Since the option exists to not have any operation, I think that is what makes it an argument.