Izzet Affinity fields lots of small creatures like Pinnacle Emissary's 1/1 Drone tokens, Emry, Lurker of the Loch, and Council of Reeds, all of which die to Massacre's -2/-2. It will not kill Pinnacle Emissary itself or Kappa Cannoneer, so those need to be answered another way. Since they have no Plains, Massacre has to be cast for its full mana cost, and it hits our creatures too, though our big reanimation targets are large enough to survive it. Surgical Extraction can exile an artifact they are trying to recast with Emry from their graveyard, along with the other copies in their hand and library, which disrupts their graveyard recursion plan. Unmask and Collective Brutality's discard modes are much weaker against an artifact-based deck with few relevant cards to strip from hand. This shifts us toward a sweeper-plus-graveyard-disruption plan while keeping our reanimation core untouched.