The Case for Theism

[Cyberman]

The problem is you can't use a theory to support yet another theory.

Why not?

A theory is an idea or a concept that may or may not be true. To support a theory you cite facts that comport with that belief which is considered evidence in favor of your belief (or hypothesis). You don't improve your lot to offer yet another unproven idea in support of your hypothesis since the theory your offering is also suspect.

Except that's not true. You're throwing around words like 'theory', 'belief' and 'hypothesis' as though they're the same thing. Do I really need to post the NCSE definitions again?

• Fact: In science, an observation that has been repeatedly confirmed and for all practical purposes is accepted as “true.” Truth in science, however, is never final and what is accepted as a fact today may be modified or even discarded tomorrow.
  
  
• Hypothesis: A tentative statement about the natural world leading to deductions that can be tested. If the deductions are verified, the hypothesis is provisionally corroborated. If the deductions are incorrect, the original hypothesis is proved false and must be abandoned or modified. Hypotheses can be used to build more complex inferences and explanations.
  
  
• Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances.
  
  
• Theory: In science, a well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses.
  

You may also find the University of Central Florida's cosmolosgy web notes "What is the scientific method?" helpful. I recommend checking out the whole section, actually.

And you most certainly can use one theory to support another theory; in fact most of the time that's how science works. For example, Big Bang Theory (not the shitcom) not only derives from the Theories of Gravity and General Relativity, it would not and could not even exist without them.