Defending yourself isn't against basic morality.

The reason there are rules to warfare is to prevent unnecessary and needless loss of non-combatant life. Once a country has broken those rules, they will be royally screwed. As for the article, I don't agree with the example they chose. The MK15 is an incredibly useful tool that helps in preventing soldiers from being killed by indirect fire. I personally know of an experience where 30 soldiers would have been killed by a mortar had the MK15 not hit it.

I think the idea is that both sides agree to not use excessively brutal methods, which serves as a win-win for both sides. As neither side has to deal with the moral issue of having their own troops get their faces burned off or something.