Because it makes high promises and ends up falling short. It imposes on itself, among other things, a need to have a working understanding of what atheism is. And it fails completely at fulfilling that self-imposed duty.why is Quran invalid? can you back your assertion with the error or invalid content from Quran?
or do you claim so just because you don't trust it?
Seeing what it says and learning that it does not deserve my trust seems plenty enough, don't you think?