Well, obviously gaara isnt afraid of anyones blood but his own. maybe its because hes lived his whole life protected by the sand shield, and when he got chidoried (lol) he freaked out because he finally saw his own blood. Besides, he even said that he kills because it makes him feel alive, so he wouldnt be afraid of blood altogether, but just his own. i mean, come on! his dad has been trying to assassinate him since he was 6!!