Like other's said, it was good that Jake decided to follow what was in his blood, even unreluctant as he was at first to be a leader.
In my opinion, the 2 packs are protecting separate things. Jacob's pack is protecting the Cullens & Nessie while Sam's pack is concerned to protect the tribe & the other humans around. Even though both know that the Cullen's will not hurt anyone but I think it's the possibility of other vampires coming to Forks that don't understand or abide by how the Cullen's live.











