The Sorcerer Supreme should defend the world at all cost, not meddle with inferior secondary squabbles. Dr Strange himself saw that Vampires pose a threat to MU and he stopped them by a spell. He easily could "weave" a spell to have peace on earth and etc etc but that doesn't threat the human race: only when hostile "powers" enters in to the fray , SS should stop that threat. A thread could be demons, vampire not a general idea like war or peace or disease (this can't be solved this is meddling with the inner workings of the universe - people need to decide for themself for war and peace ior they can cure famine and disease etc )
Remember that Sh'aar pool in his basement; He needed 5 people to close it down , he rebounded his spell on all five of them creating a pentagram closing the "pool" err rift
Also he must ally himself with the three Gods (Vishanti, Agamotto and Hoggoth) of the Temple of Three who organizes each 100 years a selection of the Sorcerer supreme.
He also belongs to the Magic of Order (as told in the Realms of Magic books by MSH - TSR)
Strange did ally himself one in occasions with demons but that was for his own good : he had to revoke his 3 allies
Later they came back to him