"Let each & every Protestant denomination unite at once with one other Protestant denomination."
Should a U. S. Dictator issue such a decree, Presbyterians would find themselves overwhelmed by proposals. Methodist Episcopalians would leap to join them. So, only a little less eagerly, would Congregationalists, Lutherans, Protestant Episcopalians, Friends (Quakers). The Presbyterians would take the Methodists.
No doubt have seven major denominational groups about whom they would least like to join. Unitarians win hands down, with Friends a unanimous but distant second. Most unpopular Unitarians would have nothing but woe. Unpopular Friends, whom...