Snipers.
Sayid was the only other candidate - and I was initially extremely shocked and... annoyed that he so rashly took Mike to the captain, but - as stated by Murg and JB - within the context, and from his perspective, I don't think he's made such an illogical decision: based on Sayid's experiences he has no reason to trust Ben, or Mike, or distrust the Captain.
To be honest, I'm not even convinced he made the wrong decision and I have the ability - as a show-watcher - to see things Sayid can't!
