Hostile armies may face each other for years, striving for the victory
which is decided in a single day. This being so, to remain in
ignorance of the enemy’s condition simply because one grudges the
outlay of a hundred ounces of silver in honors and emoluments, is the
height of inhumanity.
The paragraph above is taken from The Art of War. I have a hard time understanding what “to remain in ignorance…, is the height of inhumanity” means.
The height of inhumanity means the in the most inhumane manner or the most extremely cruel, brutal behavior, (a crime against humanity)
Sun Tzu’s argument is: war always brings frightful misery and vast expenditure of blood and treasure. A war may drag on for years unless you are kept informed of the enemy’s condition, and are ready to strike at the right moment. The only way to get this information is to employ spies, and it is impossible to obtain trustworthy spies unless they are properly paid for their services. But it is surely false economy to grudge a comparatively trifling amount for this purpose, when every day that the war lasts eats up an incalculably greater sum. This grievous burden falls on the shoulders of the poor, (referred to earlier as “men lacking at the plough-tail”) and hence Sun Tzu concludes that to neglect the use of spies is nothing less than a crime against humanity.