apostasy
Apostasy is the active repudiation of a religion, and has, generally, a negative association. A person who had experienced a de-conversion would not generally refer to herself as an “apostate”—especially as apostasy has been, at certain times and in certain traditions, a capital offense (note, for example, Deuteronomy 13:6-10, which calls for the killing of apostates: And thou shalt stone him with stones, that he die; because he hath sought to thrust thee away from the LORD thy God).
The word derives from the Greek apostasia, meaning “defection from”