A case for positive atheism

[Tiberius]

My problem with this is that it's unclear how this is different from agnosticism. Agnostics aren't sure whether God exists or not, but they lack belief in a god as much as they lack disbelief.

And so in the first paragraph, you admit that you don't even know what agnostics are. Agnostics are people who hold that the existence of God is an unknown (and in some strong cases, unknowable). They may believe that God exists (as our fr0d0 does), or they may not believe that God exists (as I do).

To explain it in a simple way, atheism / theism is all about belief. Agnosticism / gnosticism is all about knowledge. Two very different things I think you'll agree.

1) The human mind can conceive of an infinite, or at least very large, number of things.

I don't understand the first point. The differences between "infinite" and "very large" are staggering, so why the reference to both? It should be quite obvious that the human mind cannot conceive of an infinite, given that our minds are finite. That we can understand concepts of infinity doesn't mean we can imagine what an infinite amount of something looks like. Indeed, human minds can only imagine around 6 objects before we have to start grouping them (i.e. for 7, usually the groups are 3 and 4). No amount of finite groups can ever add up to an infinite.

2) There is no necessary correspondence between these ideas and reality. We can easily demonstrate this, because I can imagine there being a giraffe on my desk, but there is not. Nor are there any skunks, perpetual motion machines, 12th century minstrels, or purple fairies called Gerald.

How do you know? How can you tell there isn't a giraffe on your desk, or skunks, or perpetual motion machines, etc? To go further, how do you even know there is a desk in front of you?

3) Only if there is evidence for a particular idea is its existence in reality probable.

Not true. Before people even had ideas about pulsars, they existed in reality (at least that is what our science tells us). Existence isn't based on the evidence; existence is or it isn't. You can have as much evidence against something as you like; it doesn't mean it doesn't exist. Same with having evidence for the existence of something.

4) Because there are so many things we can think of, none of which is necessarily real, what we think of is very unlikely to be real.

Non-sequitur. Simply does not follow that because we can think of a lot of things, the chances of them being real is very low. Us being able to conceive of things has no effect on their existence, or even their probability of existing.

5) There is no evidence, or no good evidence, for God's existence (this, of course, could be disputed, but that's no doubt been done and dealt with elsewhere).

Ok by me.

6) The concept of God is very unlikely to exist in reality.

Not true. Absence of evidence is not evidence of absence. There is no evidence that the Higgs boson exists; absolutely none at all. The only reason we are looking for it is it's existence would fix some holes in the standard model, but there is no direct evidence it exists. This doesn't mean it is very unlikely to exist, nor does it mean it is very likely to exist. All it means is that as of this moment in time, we do not know if it exists. Existence isn't a probabilistic thing.

7) Ergo.. there probably is no god.

Since the argument is fatally flawed in several locations, the conclusion it draws is unsupported.