The answer to this question is number 5, "all of these". The American Anti-Imperialist League was formed on June 15th, 1898, to challenge and organize against the Spanish-American War. The American Anti-Imperialist League formed in opposition particularly to the United State's military invasion of the Philippines as they stood firmly against imperialism and the creation of an American empire. The league posited several arguments against US imperialism. One of these arguments was moral in nature and rooted in enlightenment era principles and political theories. This argument stated that imperialism was contrary to the principles of a republic, and that the United States could not truly claim to honor individual freedom and pursuit of happiness while denying the national sovereignty and individual freedoms of Filipino people. If a republic requires the active participation of citizens, then forcibly claiming the Philippines as US territory strictly ran counter to the claims of being a republic.
In addition to the League claiming that the US could not be both a republic and an empire, it also pointed out that invading another people ran counter to democratic people in which people are supposed to be able to elect their chosen representatives. By invading the Philippines and claiming it as US territory, Filipino people are denied the ability to vote in accordance to their own governance system.
The American Anti-Imperialist League also took the position that imperialism weakened union strength and strength of American workers in general if American companies could simply pay workers in the Philippines less for the same labor and production. This position was posited from a less moral stance, and a much more nationalist position. This position was less concerned with the injustice of paying Filipino workers less and more concerned with the possible ramifications of outsourcing labor for American workers.