The only way failing to save lives can be equated with killing people is by subscribing to pure utilitarianism. But by that philosophy, contraception is also equivalent to killing people:

Naive total utilitarianism implies that - which is why I don't follow it. But you can have more complicated utilitarianist systems where failing to save lives is equivalent with killing people (and thus bad) while contraception is perfectly fine and in some cases laudable. That's close to the system I'm currently trying to formalise; we'll see if it works.