I'm reading a book, and the antagonist was released from prison early because he bribed the district prosecutioner.
The main character says: 野郎。。。 法なんてあってねーようなもんじゃねーか
This is my translation: Bastard... It's like there is no law (lacking in lawfulness?)
But I'm not sure how もんじゃない functions here. I know もんだ/です can function as giving a reason for something. Is もんじゃない used similarly but ない is used because it is a negative verb?