Shia Islamic Argument for the existence of God

[GrandizerII]

Bold mine. Why must there be such an extension? Will basic reality not suffice?

Here the word "absolute" is synonymous to "infinite". Why must its extension be an infinite reality? That has been explained before, in the part that says that the extension of this reality cannot be the finite beings, their totality, and their universals. Since its extension cannot be among the finite beings, it logically follows that the extension must be an infinite being. Also, let's be careful about not making judgments or understanding the nature of this "reality" prior to logically analyzing its extensions as the argument does.

Why infinite being? Why not infinite something instead?

Ok, I see you address this later on.

Since the entity is absolute/infinite, nothing limits it, and it cannot have any lacks; it must possess all and every degree of existence. Consciousness is a degree/aspect of existence (a rock that is conscious has more existence than an unconscious rock), and since the entity cannot lack anything, it must possess infinite consciousness. The same can be said for knowledge."

Here, it seems you are making the mistake of presuming only one broad type of "infinity". I think "infinity" is a vague word we use to try to capture multiple areas of "unlimitedness". You could apply the word to boundless space, boundless time, boundless love (infinite love), boundless afterlife (eternal heaven and hell), boundless evil, and so on.

Nothing in your argument suggests that an infinite reality (in terms of space and time, I'm guessing) must have any of those other infinite qualities.

Also, knowledge could be a sign of "limitedness" rather than "infiniteness" as you don't need to know anything if you're infinite in space/time.