Griefers aren't a large problem (at least in the servers I have been playing in) and are nothing a quit votekick/ban cannot fix.
To your assertion that any sensible soldier would simply stay their hand if their friend were to jump in the way of their strike, the current situation with shields is just that--the game just assumes that any shield wielder will block all frontal attacks, thus removing any requirement of focus or skilled use of shield coverage by the player. It also makes archery a lost cause when fighting someone with a shield. The community has taken notice of this disturbing phenomena, and sentiment is nearly unanimous that the player should have to be conscious of where he is putting his shield, and that this disconnection of the player from his in-game self is a detriment to gameplay. Why then, should the player just think, "Oh, my friend jumped in front of me, I'll just keep swinging. Surely my digital self will pick up the slack." Your friend's untimely death would normally teach him to give you space, thus allowing you to get more attacks in.