Best books debunking Christianity

[Neo-Scholastic]

Personally, IMO, from a purely intellectual point of view, nihilism is the ultimate conclusion of any philosophy without some grounding in the Divine. I cannot say that definitively, since I cannot exclude the possibility that some historic or current atheistic philosophy of which I am unaware avoids it.

Doesn't Plato's Euthyphro argument avoid it? Plato actually seems to argue the reverse: that assuming values just because "God says so" represents a nihilism of sorts.

Plato contrasts the arbitrary will of the Greek pantheon with the ultimate Ideal. This concept is further developed not only by Aristotle but by other Platonists like Plotinus. Thus we get the God of Classical Theism. The Scholastics considered this pretty much the limit of what could be known of God apart from special revelation. So the difference is this. The gods of the Greek pantheon would issue commands of the "Because I said so" variety; whereas the Christian God says, "Be perfect as I am Perfect" which aligns nicely with the Platonic notion of "The Good".