Yes, such a group actually existed back in the day, and Mark Twain was a member. Below is part of the Anti-Imperialist League's mission statement, which refers to the American annexation of the Philippines and the Philippine-American War:
We deny that the obligation of all citizens to support their Government in times of grave National peril applies to the present situation. If an Administration may with impunity ignore the issues upon which it was chosen, deliberately create a condition of war anywhere on the face of the globe, debauch the civil service for spoils to promote the adventure, organize a truth suppressing censorship and demand of all citizens a suspension of judgment and their unanimous support while it chooses to continue the fighting, representative government itself is imperiled.
We hold, with Abraham Lincoln, that "no man is good enough to govern another man without that man's consent. When the white man governs himself, that is self-government, but when he governs himself and also governs another man, that is more than self-government--that is despotism." "Our reliance is in the love of liberty which God has planted in us. Our defense is in the spirit which prizes liberty as the heritage of all men in all lands. Those who deny freedom to others deserve it not for themselves, and under a just God cannot long retain it."