As regards the pissing thing, I recognise that it makes for a public relations mess. But war is what it is. It's kinda nasty. And the psychology is extreme and complicated. Wars are not fought by nuns. These sorts of things happen.
For some reason, these Marines needed to express their contempt. They did so. And everyone is up in arms about the disrespect they are showing for the corpses. We live amongst common taboos and breaching them has consequences.
If I was one of those Afghans being pissed on, however, I think the being dead bit is worse than the soaking.