The judge did not base his argument on an abstract mathematical modeling of the entire setting but rather on the consequences. If such clubs indeed cause people to lose everything leaving their families destitute we must conclude that the overall setting makes this activity mainly a gambling activity and that this game is mainly a game of luck (in the same way playing the roulette is).

By this "argument", financial investing is mainly a gambling activity and mainly a game of luck, since it's just as obviously the case that such markets "indeed cause people to lose everything leaving their families destitute."