Necessary Thing

[Ignorant]

Further, it's assuming everything behaves in a "building block" manner like this. Contingency just means if one thing goes, so does the other.

Yes, but the fuller meaning includes an existential and unidirectional dependence between the two. Helium depends on the existence of protons, but protons do not depend on the existence of helium: therefore, protons ARE NOT contingent upon helium.

To just assume all things work like atoms is this extrapolation error I keep referring to.

I don't assume that all things work like atoms. If I did, my premise would read "ALL things exist on the condition that another thing exists synchronously". Instead, I use "some" rather than "all"

This reality could be one tiny pin prick in an infinite series of nested realities, each one contingent on the next.

Yes it could. Above, I consider that possibility, and find it logically contradictory. Can you point out why the apparent contradiction is not in fact one?

But you can't just say "no it can't be that way because of what helium is like". I don't have to show things are this way, just that it is a logical possibility the premises don't account for.

I recognize the logical possibility in the sense: either there are an infinity of conditions or not for a finite thing's existence.

When I consider that possibility in the affirmative, I find it logically contradictory. You don't have to show me an infinity of conditions, but I would like to know how an infinity of conditions are possible in a finite thing.