[idofgrahf]

Fighting for "Justice" and protecting people is good but whats the point if you die basically a dogs death and still not accomplishing your goal? ( which would be the case if shirou is to fight any of the servant at his current level). I think its pretty obvious that you can't protect anything when you are dead, (unless as a gost? like in Bleach?) but then again Shirou isn't the smartest guy around.

My guess is that he doesn't want saber to fight because of the battle with Hercules, Saber was pretty beat up in that one and the sight was gursome as well. While I think Shirou would perfer Ren doesn't fight as well, he is not as insistant because one he can't do anything about it and second, he has yet seen Ren get almost cut in half yet. After all, seeing is believing.