I should have linked this article in the post, but I address it here.

Basically, since freedom is the foundation of morality, and others have freedom, the only way to create a moral system is through a social contract. The contract respects the freedom of others as it would include principles that cannot be reasonably rejected by free people.

So one's freedom to kill isn't moral, not because of the utility consequences, but because it doesn't respect another freedom by failing to abide by the social contract.