I'm not an atheist, but here's a truncated version with slight modifications from the Spinozan original. The upshot being that dualism is bunk and monism rules. This leaves us with a situation -- there is an originary substance, but we cannot know that substance in itself. We can view that substance as divine (as Spinoza chose to do) or we can view it as profane. We are left with a choice, really, with no means to decide.
Take the red pill or the blue pill. It is your choice. It is just as rational to choose one or the other.
It is not rational to limit your choice to particular attributes once the choice is made -- in other words, making God in your own image is not rational. Any anthropomorphization that fixes God into some type, be it "the designer" or "the Christian God" is a limitation on God's attributes.
Prop. I. Substance is by Nature prior to its modifications.
Premise 1. Substance exists and cannot be dependent on anything
else for its existence.
Prop. II.
Two substances, whose attributes are different, have
nothing in common.
Premise 2. No two substances can share an attribute.
Proof: If they share an attribute, they would be identical. Therefore
they can only be individuated by their modes. But then they would
depend on their modes for their identity. This would have the sub-
stance being dependent on its mode, in violation of premise 1.
Therefore, two substances cannot share the same attribute.
Prop. III. Things which have nothing in common cannot be one
the cause of the other.
Premise 3. A substance can only be caused by something similar
to itself (something that shares its attribute).
Prop. IV. Two or more distinct things are distinguished one from
the other, either by the difference of the attributes of
the substances, or by the difference of their modifica-
tions.
Implied is Premise 4. Substance cannot be caused.
Proof: Something can only be caused by something which
is similar to itself, in other words something that shares its
attribute. But according to premise 2, no two substances can
share an attribute. Therefore substance cannot be caused.
Prop. V. There cannot exist in the universe two or more
substances having the same nature or attribute.
Implied is Premise 5. Substance is infinite.
Proof: If substance were not infinite, it would be finite and
limited by something. But to be limited by something is to be
dependent on it. However, substance cannot be dependent
on anything else (premise 1), therefore substance is infinite.
Prop. VI. One substance cannot be produced by another
substance.
IImplied is the Conclusion: There can only be one substance.
Proof: If there were two infinite substances, they would limit
each other. But this would act as a restraint, and they would
be dependent on each other. But they cannot be dependent
on each other (premise 1), therefore there cannot be two
substances.
Prop. VII.
Existence belongs to the Nature of substance.
Prop. VIII
Every substance is necessarily infinite.
Prop. IX. The more reality or being a thing has the greater the
number of its attributes.
Prop. X. Each particular attribute of the one substance must
be conceived through itself.
Prop. XI. Substance, consisting of infinite attributes, of
which each expresses eternal and infinite essentiality,
necessarily exists.
Prop. XII.
No attribute of substance can be conceived from which
it would follow that substance can be divided.
Prop. XIII. Substance absolutely infinite is indivisible.
