Early on, Lord Acton developed the central theme of his life. This was the idea of conscience. The most important garauntee of freedom is that every individual has an educated conscience. He called liberty the reign of conscience. True freedom can exist in the world when every individual is free to exercise that conscience, and that conscience has been educated in a free fashion.
Papal infallibility is the exact opposite of that. If the Pope is infallible then you cannot question his authority. Lord Acton was a devout Catholic. Through his study of history, he said this is absolutely contrary to the teachings of the church. If you look through Church history, there has been a very powerful role played by church councils. Like Socrates, Acton got deeply involved in the Papal politics, but he was defeated, even though he met bishops and high churchmen who has said they opposed Papal infallibility, but they went along with the crowd when he needed them. In other words, they denied their conscience and did what was expedient. Acton was nearly excommunicated.
What I’m going to say next came to a surprise to me when I first found out. Acton supported the American South during the Civil War. He loved the United States, and was one of the first Englishmen to realize that the Declaration of Independence and the Federalist Papers were political literature worthy of comparing to Plato and Socrates. In Britain people assumed that America was a democracy, exhibiting all the worse characteristics of the Athenian Democracy. It was a radical democracy with no checks on the will of the people. Acton said that America was a balanced Constitution, and the supreme balance was the rights of the States. It is indeed a Confederation of States, and in the power of the states will always lie a check upon a centralized radical democracy. For a centralized radical democracy will be imperialistic abroad and despotic at home.
Lord Acton never had a university degree. He read Plutarch and the classics. He developed a keen sense for 19th century progressive history, which focused upon the use of original documents. He wanted to have an active role in the Catholic Church, and bring the Church into the 19th Century. In his series of magazines he denounced the church for supporting autocratic governments instead of democratic ones. It was in one of these magazines, then, that I believe he wrote his famous dictum, “Absolute power corrupts absolutely.”