Drones have agency; they can target precisely and evade defense mechanisms, whereas gas spreads in well understood and constrained ways. You can't release a cloud of sarin or anthrax over Washington DC and instruct it to seek and destroy the entire high-level leadership of the US government. With drones, you can. And it doesn't require superintelligence, just face recognition at the level that already exists, and some engineering work to put all the pieces together.

Is a drone attack worse than a nuclear detonation or mass biological attack? Maybe not. But if you haven't noticed, people are scared shitless of nuke and bioweapon attacks, and with good reason. So it doesn't seem unreasonable to question whether we should be directing government resources towards developing weaponized drone technology that will inevitably be used against us.