Why did Queen Elizabeth I forbid Catholicism?

Answer 1

Short answer: politically she had no choice. Henry VIII"s first wife, Queen Catherine of Aragon was his only legitimate wife, and due to Henry's infertility problems, she had only given one daughter, Princess Mary, and no other children. Henry was having an affair with Anne Boleyn, which was doubly scandalous as Henry had previously had an affair with Anne's mother, and her husband confided to Henry that he could not marry Anne Boleyn as she was actually his natural daughter, but he did anyone as Anne was pregnant and Henry was hoping for a son.

So He got the Archbishop of Canterbury to declare his marriage to Catherine null even though the Pope had specifically ruled that it was valid. Thus when Elizabeth I came to the throne through Henry's will, she was technically illegitimate and couldn't inherit the throne according to the Catholic Church. Thus Henry had already moved away from the Catholic Church in order to secure his line of succession and Elizabeth either had to give up the throne or outlaw Catholicism.

At that time in history, after the Peace of Westphalia, ruling princes in Europe assumed that their subjects had to be the same religion as they were, and to be Catholic or Protestant was not so much a religious choice (in their eyes) but a matter of treason or obedience to the crown. Thus Elizabeth continued her brother and father's habit of executing Catholics who refused to leave their religion and renounce Catholicism.