I mean, the potion is a biological weapon, and the US, having eliminated its biological stockpiles and spent thirty years and counting destroying its chemical weapon stockpiles, has the policy of "a WMD is a WMD, and the only WMD we have to retaliate with is nuclear, so that's what you get" so it's not as if the use of nukes on Equestria is entirely out of order, but, unless I missed something, these are not heads of state making that decision, and no, I don't believe that the use of WMDs should devolve to a head of government when that's not the same person.