Cervantes once wrote in his Don Quixote:
Love looks at things through spectacles, turning brass into gold, poverty into wealth, and specks in one's eyes into pearls.
There were no specks in Severus's eyes, but there was indeed a Death Eater mark on his arm. Pomona was not blind enough to mistake it for a pearl.
During the grand trial, he had gone to XZ with her. Even if Karkaroff had exposed him then, the Ministry of Magic would have had to cross half the globe to arrest him.
Voldemort was not an internationally wanted criminal like Grindelwald. Though he had quite a few foreign supporters, it was no longer like the 1920s, when British Aurors could cross borders and go wherever they pleased to hunt someone down.
If they wanted to capture Severus across national borders, they would need to go through the International Confederation of Wizards, and Albus Dumbledore was its president.
But things were different now. He was right here in Britain, and she had no idea what he had been thinking, to actually treat Habeas Corpus as a "talisman."
Habeas Corpus had indeed been effective over two hundred years ago. It had been established according to the Magna Carta, which stated that no one could be imprisoned without lawful judgment or the law of the land.
For instance, in 1615, a prisoner was incarcerated by the Court of High Commission for making blasphemous remarks. The ordinary courts believed there was no evidence that he had said those words, so they issued Habeas Corpus and sent him to stand trial in an ordinary court.
King's Bench could issue Habeas Corpus to release a prisoner on the grounds that the Court of High Commission had no authority to punish anyone with imprisonment. In matters of state, no one