The argument from degree

[Objectivist]

Aquinas: [T]he maximum in any genus is the cause of all in that genus; as fire, which is the maximum heat, is the cause of all hot things. Therefore there must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God. 

I answer that:

A bachelor has a least dirty shirt in his apartment, which is a tautology, but it does not follow that he has a clean shirt. The being with the greatest perfection is not necessarily a being with infinite perfection.

I like your answer.  I've also heard that an even greater being could do all of the things that gods are supposed to do but it could do them while not existing, therefore god does not exist.  

Aquinas' argument is total rationalism or reasoning above facts.  The first cause is existence qua existence.  Where does life come from?  Existence.  Where did the earth come from?  Existence.  Where does consciousness come from?  Existence.  It's existence all the way down.  Where did existence come from then?  Blank out.  There's nowhere for it to come from or go to.