Mr Light wrote:
Or blow his brains out. Zombie rule.
I can only assume that Sayid was seriously not right in the head when he did this, either through the trauma of returning to the Island seeing Young Ben or the "truth serum" or a combination of the two, because I really felt that he was out of character in this episode.
I thought the scene where he shot lil Ben was played so that we were supposed to regard Sayid as being almost completely out of it. Without the truth serum, he probably would have restrained his impulse to kill lil Ben.