And the Destroyer was wiping out the town, which didn't have anything to do with who got to rule Asgard. Loki didn't tell it "Go keep Thor from coming home," or even "Kill Thor;" he told it to "Destroy Everything," thus murdering a bunch of random people in the town (and anyone know what happened to the SHIELD Agents besides Coulson?). Or he would have had Jane and Thor not evacuated the town.