This post is not concerned with the question of whether or not God exists. Rather, I wanted to point out the two main fallacies in the reasons given for belief in God that I've seen cited almost word-for-word everywhere from Jehovah's Witness tracts to Internet sites. Here's a good example, that pretty much covers all of the bases:
Fallacy number one:
a.) "Most of the things I've encountered in my life which appear to have been designed by a thinking designer were, in fact, designed by a purposeful designer. Therefore, all things which appear to have been designed must have been designed by a purposeful designer."
b.) "The chain of causation cannot, logically, go back forever. Therefore there must be a first cause, and this first cause must be God."
There is, no doubt, a fancy-sounding Latin term for this particular fallacy, but in common parlance it's what's known as "jumping to conclusions". It's true that many things we encounter which appear to have been designed were, in fact, designed. However, to jump to the conclusion that all things which appear to have been designed must have been designed is the same as saying: all swans I've encountered have been white. Therefore, all swans are white.
The fact of the matter is that while many things which appear to have been designed were designed, all evidence supports theories that indicate that many things we encounter, although appearing to have been designed, were not, in fact, designed. They are the product of complex but un-purposeful interactions, and merely have the appearance of having been designed.
Similarly, it's true that the chain of causation cannot extend backward unto infinity. If that were the case, we would never have arrived at this moment, since it would necessarily be preceded by an infinite amount of time. However, to tout this as "evidence" of God's existence is to jump to conclusions. There are many philosophies which deal with the subject, as well as popular religions like Buddhism and Taoism which offer atheistic explanations.
Fallacy number two:
"DNA / cells (Jehovah's Witnesses love this one) / the earth and its environment / the cosmos / etc. are so complex! Look at how complex they are: [various data about DNA / cells / the earth and its environment / etc.] I can't believe something so complex could have simply arisen. Therefore, they must have been created by God."
This is known as the Argument from Incredulity, which could be summarized as: I find theory B difficult to conceive of, personally, therefore theory A is correct.
It's true that all of the things cited above are very complex, and that the idea that they arose from un-directed, un-purposeful and complex interactions is counterintuitive and difficult to imagine, but that is what all evidence thus far indicates. Of course, people will again point to specific parts of specific scientific theories they find difficult to fathom, citing this as "evidence" that God exists, but you could just as easily say: evolution strikes me as a crock. Again proving that, as I have been saying all along, the universe is turtles upon turtles all the way down.
The point is that even if all of science turned out to be mistaken (which is difficult to imagine but not impossible), the "God theory" would not suddenly prevail. It would just mean we would be back in a position of having no plausible theories supported by evidence.