In the case of a clearly signified medic helping, no.
Unfortunately, from what I hear, in the heat of battle it's not always easy to determine what's happening in such situations.
When you've been trained to fight the enemy and you're rushing headlong into battle, missiles of whatever type (bullets, arrows/bolts, explosive shells, etc) are wizzing past you, much of the time I'm sure it's all too easy to get caught up in the moment and just attack on instinct rather than hesitate and risk being killed yourself.
In all honesty, I'm not much of a fighter in that sense, so I can't really tell what I would do in such a situation. If there was someone left screaming in pain without medical aid or companions to help them, the most I would offer is a mercy killing... though knowing me, if it were a situation where it was just me and the wounded, enemy or not, I'd probably end up doing what I could to help them rather than just kill them.