What amount of disutility does creating a new person generate in Negative Preference Utilitarian ethics?

I need to elaborate in order to explain exactly what question I am asking: I've been studying various forms of ethics, and when I was studying Negative Preference Utilitarianism (or anti-natalism, as I believe it's often also called) I came across what seems like a huge, titanic flaw that seems to destroy the entire system.

The flaw is this: The goal of negative preference utilitarianism is to prevent the existence of unsatisfied preferences. This means that negative preference utilitarians are opposed to having children, as doing so will create more unsatisfied preferences. And they are opposed to people dying under normal circumstances, because someone's death will prevent them from satisfying their existing preferences.

So what happens when you create someone who is going to die, and has an unbounded utility function? The amount of preferences they have is essentially infinite, does that mean that if such a person is created it is impossible to do any more harm, since an infinite amount of unsatisfied preferences have just been created? Does that mean that we should be willing to torture everyone on Earth for a thousand years if doing so will prevent the creation of such a person?

The problem doesn't go away if you assume humans have bounded utility functions. Suppose we have a bounded utility function, so living an infinite number of years, or a googolplex number of years, is equivalent to living a mere hundred billion years for us. That still means that creating someone who will live a normal 70 year lifespan is a titanic harm, a harm that everyone alive on Earth today should be willing to die to prevent it, as it would create 99,999,999,930 years worth of unsatisfied preferences!

My question is, how do negative preference utilitarians deal with this? The ones I've encountered online make an effort to avoid having children, but they don't devote every waking minute of their lives to it. And I don't think akrasia is the cause, because I've heard some of them admit that it would be acceptable to have a child if doing so reduced the preference frustration/suffering of a very large amount of existing people.

So with that introduction out of the way, my questions, on a basic level are:

1. How much suffering/preference frustration would an antinatalist be willing to inflict on existing people in order to prevent a birth? How much suffering/preference frustration would a birth have to stop in order for it to be justified? For simplicity's sake, let's assume the child who is born has a normal middle class life in a 1st world country with no exceptional bodily or mental health problems.

2. How exactly did they go about calculating the answer to question 1?

There has to be some answer to this question, there wouldn't be whole communities of anti-natalists online if their ideology could be defeated with a simple logic problem.