Is nihilism the logical extreme of atheism?

[genkaus]

Well-argued. Put like this, the errors of your reasoning become much clearer.

Reality is flawed.
Reasoning from it is limited by those flaws.
Hence the atheist position

Premise 1 is incorrect - the concept of flaw or perfection does not apply to reality unless there is an assumption of supervening consciousness. That's an assumption atheists do not accept - so if you want to establish your position as true, you need to bring evidence for god. Without it reality is neither flawed nor perfect.

God is perfectly just
Reasoning from God reasons a just reality.

This is the part where fantasy leads to more fantasy.

The two assumed beliefs here are "god exists" and "he is perfectly just" - and the logically valid conclusion would be that it results in a "just reality". But since a just reality is not evident, either one or both of your assumptions are wrong. To get around this, you fantasize about a just reality by dreaming up heaven and hell.

Human flaws exist. We are only capable of perfect justice given our inclusion of God. If we fail, then yes, it doesn't work. No problem there. This is what we deal with.

Human flaws would mean flaws in human reasoning as well - so irrespective of your god's existence, the flaws in reasoning would render humans incapable of perfect justice even with the inclusion of god.

"Christian" not acting as if God were just are exactly the same as atheists. You're not disproving Christianity by saying that people failing at Christianity define it. They don't.

It disproves your capacity for perfect justice.

Mainstream Christianity as I practice and accept it encompasses many interpretations that the church body accepts as valid. Some interpretations are judged to be flawed, like Mormonism, and are not accepted.

Accepting contradictory positions as valid call into question the soundness of argument and the truth of the premises.

Evidence of God isn't in question. Only belief is.

Simple belief in god would only go so far to establish belief in the idea of perfect justice. To establish actual existence of perfect justice, you'd need to provide evidence for the source. And if your argument is limited only to the belief in the idea of perfect justice, then those fantasies are of little use to the real world.