What does "one cannot justify war unless each side flaunts its own blind conviction." mean?

This means that there is no reason to go to war unless both sides of the argument are unable to see and understand what the other side is trying to justify. Having a conviction in a cause or a belief without looking at the other side of the coin and trying to understand what might be seen as an uncomfortable viewpoint is what often leads to skirmishes and wars.

The dangers of an inadequate monetary supply.