Prisoner of conscience
A prisoner of conscience is someone who is being held prisoner for their political/religious beliefs and/or their advocacy thereof. As originally defined, that person had to be arrested and held for the non-violent expression of their beliefs, or for reasons of a protected status (race, religion, sex, orientation, or language.) The very term was created by Amnesty International, a very respected human rights organization. When used by AI, and in most uses around the world, this is a significant human rights violation.
To a certain extent, however, it has become a loaded word, because it implies that the person is being held unjustly for the sole reason that they hold certain beliefs. However, there have been cases of people who have espoused violence against other groups (or even engaged in it) who have then been arrested as a danger to the public. While technically they do not qualify for "prisoner of conscience" status (as defined by AI), many claim it anyway. This is similar to how homophobic preachers scream "religious discrimination" when others push for civil rights for homosexuals. Many violent racists try to claim this status when they are put away for plotting violence.