Four arguments against the existence of God

[Simon Moon]

...the unmoved mover has never been demonstrated to exist, and thus lacks any form of justification,...

Summa Theologica, First Part, Question 2, Article 3 demonstrates the necessity of an unmoved mover, as part of the "1st way."

Do you mean:

1. Our senses prove that some things are in motion.
2. Things move when potential motion becomes actual motion.
3. Only an actual motion can convert a potential motion into an actual motion.
4. Nothing can be at once in both actuality and potentiality in the same respect (i.e., if both actual and potential, it is actual in one respect and potential in another).
5. Therefore nothing can move itself.
6. Therefore each thing in motion is moved by something else.
7. The sequence of motion cannot extend ad infinitum.
8. Therefore it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

Isn't this just the first cause argument with word 'motion' being substituted for 'cause'?

Seems to me that it has the same flaws as every first cause argument.

Why can't something be in motion on its own?

It also assumes, without justification, that there can only be one unmoved thing. Other than to fit the presupposed definition of his god, what is his justification?

He also seems to be guilty of affirming the consequent. In other words, he is saying that there are 2 sets: one that contains moved things, and one that contains unmoved things.

To be meaningful, a set can't be empty, but more importantly, it has to have more than one object, or it is nothing more than a synonym for whatever is being argued for.

So, unless he allows for more than one unmoved mover to be in the set, he is just smuggling his god in the premises.