I understand why B is right, but for the sake of consistency, would the not in answer choice D not cause necessary negation, to become: "If every member of the city council abstains in the vote on the proposal, the matter will be decided by city voters.

This would follow a similar pattern to others, where it is just restating a premise.

This was the most absurd LSAT question that I've come across yet.

This section on flaws needs some serious work. Videos would help clarify things to a greater degree than these pitifully written explanations. I had to go to another site to get clarification.