These books were written hundreds of years past, and compilation may have streached out over hundreds of years. The authors, dates, and inspirations are impossible to know with much certainty. They were written by people, and people are capable of self delusion and grand visions. Meanings are changed during translation. Stories inherited orally vary with each telling. If today someone publicly claimed they were a religious prophet, and knew the word of god, almost everyone would doubt that claim. Why should we have less doubt about claims made hundreds of years in the past. The claims made in these books lack verification from other sources of the same period. Quoting these texts to validate their own authenticity, or to support other religious positions is not reasonable.

2. Complexity of the universe

Our universe is so complex an intelligent creator is necessary. This is a reasoning fallacy of explaining one complex mystery (the origin of the universe) with another complex mystery (a god). This is a frequent logic error in thinking about this subject, and is not an explanation. It is an attempt to explain one unknown with another.

3. The universe must have a cause

There is the claim that a god was the cause, and that god has always existed. It could just as easily be stated that the material from which the universe was formed has always existed. The first cause claim assumes that time has always existed, but if time is a property of the universe, time begin with the Big Bang. It's a difficult idea to grasp, but it's likely there was no "before" the Big Bang. No before, no cause. Our current state of knowledge cannot explain the origin of the energy or matter that formed the universe, and our concept of time is probably not complete.

4. A beautifully ordered universe

The world, and the universe, is too beautifully designed and ordered to not have an intelligent creator. There are examples that contest this view. Many animals kill and devour other animals. The earth itself has events that create death and pain to its inhabitants. There are large meteorites in our solar system that will have destructive collisions with the earth. The earth appears to exist in an beautifully ordered solar system, but it has arrived at this state only after a long period of violent global geologic activity which continues.

5. Faith

Some religious writers say faith is a gift from god, and is the only valid evidence of god. This is a somewhat circuitous statement. It declares, as irrelevant, any analysis that could introduce doubt. This appears to be a way of maintaining belief in a god by not asking questions. It requires the suspension of reason and analysis. Faith is a bypass, not evidence.

6. God cannot be disproved

It cannot be proved that god does not exist. This proof is not necessory. The burdon of proof  lies with the the claim that a god does exist.

7. Billions of believers

Billions believe there's a god, and that many people could not be wrong. Among the major religions most members of each think all the others are wrong. Once everyone thought the earth was flat, and the sun moved around the earth. Many still believe the earth is just a few thousand years old. For most of human history there was a majority that held various incorrect beliefs.