Imagine you were deciding whether or not to take an action. This action would cause a person to endure immense suffering—far more suffering than would occur as the result of a random assault. This person literally cannot consent. This action probably would bring about more happiness than suffering, but it forces upon them immense suffering to which they don’t consent. In fact, you know that there’s a high chance that this action will result in a rights violation, if not many rights violations.
If you do not take the action, there is no chance that you will violate the person’s rights. In fact, absent this action, there rights can’t be violated at all. In fact, you know that the action will have a 100% chance of causing them to die. There’s also a reasonable chance (Statistics differ about this), that it will cause them to be sexually assaulted.
Should you take the action? On most moral systems, the answer would seem to be obviously no. After all, you condemn someone to certain death, cause them immense suffering, and they don’t even consent. How is that justified?
Well, the action I was talking about was giving birth. After all, those who are born are certain to die at some point. They’re likely have immense suffering (though probably more happiness). The suffering that you inflict upon someone by giving birth to them is far greater than the suffering that you inflict upon someone if you brutally beat them.
So utilitarianism seems to naturally—unlike other theories—provide an account of why giving birth is not morally abhorrent. This is another fact that supports it.
Maybe a person thinks that most children will have more total suffering than pleasure in their lives. If that’s true, then utilitarianism would condemn it. However, that doesn’t seem unintuitive. Other theories have the harmful consequence of condemning giving birth, even if the people will live good lives overall.
What this example shows is that utilitarianism does well in morally weird cases. This is an advantage of a theory. If a scientific theory got incorrect results about the gravity on mars, it would be rightly abandoned. So the fact that utilitarianism gets correct answers across a wide range of strange cases is just one more evidential chip in favor of utilitarianism.
This is why consequentialism is absurd when taken to the extreme.