I think you have not read the rules carefully enough to appreciate the challenge of this game, > Third, each pirate would prefer to throw another overboard, if

I think you have not read the rules carefully enough to appreciate the challenge of this game, > Third, each pirate would prefer to throw another overboard, if all other results would otherwise be equal. If a pirate found themself in a situation where they thought their vote wouldn't change the outcome -- i.e. all other results would otherwise be equal -- they would vote to murder the proposer. In the situation you describe, every pirate would find themselves in that situation, and would thus vote for blood.