abolitionist
Refers to a person who advocates for the complete abolition of a system, practice, or institution, such as slavery, the death penalty, or nuclear weapons.
He is known as an abolitionist of the death penalty.
廃止論者 is a broader term for someone who advocates abolition or discontinuation of something, while 全廃論者 specifically emphasizes complete or total abolition.
Compound of 全 (zen, 'complete'), 廃 (hai, 'abolish'), 論 (ron, 'argument/theory'), and 者 (sha, 'person'). The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning 'abolitionist'.