Arguments against the existence of God

I'll begin with the argument from religious experience - I'll deal with other kinds of arguments about god in a later post, but the most common way in which people attempt to justify their belief in god is personal - they have experienced god, they have a relationship with god, so of course god exists.

Let's formalize this claim:
Argument from religious experience:
1 many people have religious experiences, which they interpret as experiences of God;
2 people’s own interpretations of their experiences are trustworthy;
thus, God exists.

The problems with this argument abound - here's a few: for premise 1, which tradition/ history of experience are we referring to? Different religions and different believer's claimed experiences make numerous conflicting/ contradictory claims, with many different incompatible theories of God proclaimed - leads to doubt that one single thing could be so multiply interpreted. At most one is right. If many are wrong, why not all?

Premise 2 is fairly obviously false - the mere having of religious experience obviously doesn’t guarantee God exists, or more to the point, guarantee that one is an accurate interpreter of one's own experience. We misunderstand what is happening to us all the time. Take, say, schizophrenia and the biblical story of Abraham and Isaac, in which God tells Abraham to kill his son... what would you say to someone who walks up to you on the street and tells you - 'God told me to kill my family'. Would you take that as proof of the existence of the divine? Or is a mental disorder a more likely (and more parsimonius) explanation?

Are there any other ways to explain religious experience other than real God? Yes –

Other arguments against existence of God - Let's start here by formalizing that first problem above:

Inductive argument from diversity of religious experience versus God:
1 many people have religious experiences, which they interpret as experiences of God, but their accounts conflict;
2 there are 10000-plus different religions, all relying on claimed experiences of the divine, all of which accounts conflict in at least some detail (or else they would be the same religion!);
3 hence, most religions and their claims about the experience of the divine are untrustworthy in at least some details about God, as at most one could be entirely right;
4 there is no rational way to decide that one faith-based claim about god is more defensible than any other (analytic, from the definition of faith)
5 hence, there is no rational reason to think any particular religion is more likely to be entirely correct than any other
6 But logic dictates that (almost) all religions make false claims about god – at most one could be correct - so (almost?) all religions make false claims about god
7 Given there’s no rational basis for choice and the vast majority are known to be false, then inductively, the only reasonable belief is that all religions and personal experiences are wrong about God - that indeed, all religions make false claims about god
5 Occam’s razor – so we don’t need true beliefs about God to explain religious belief
thus, God doesn’t exist.

Another argument versus God- Argument from Simplicity:
1 Occam’s razor/ principle of parsimony/ simplicity - don't multiply entities beyond necessity, don't believe in the existence of things that are not required for explanations
2 we don’t directly experience anything that corresponds to concept (definition) of God (cf apple, or the color orange)
3 we don’t indirectly experience anything whose best explanation is that it must be caused by God (cf electron, proton)
4 So God is not required to explain any experience we have
So no need for God’s existence – so by Occam’s razor, God doesn’t exist

And another - for the simplicity argument is connected to ‘God of the gaps’ argument:
1 we believe in a supernatural God because It explains what natural science cannot
2 so God’s attributes are traditionally given in terms of what science cannot explain – god is defined by the gaps in science
3 But the history of science shows that science progressively explains more and more things formerly attributed to God
4 Inductively, there’s no reason to think that science will not eventually explain everything that can be explained
5 So God explains nothing – and so has no attributes
So God does not exist

Compare the problem of evil (POE): argument against God from concept and consequences
1 God is 3 omnis (omnipotent, omniscient, omnibenevolent) and creator of the universe
2 Evil exists
3 God, if existing, would not allow evil (If God is 3 omnis, evil would not exist; i.e., God and evil are incompatible - (God would know how to, want to, and could prevent all evil).
Thus, God does not exist