Rewards should be bestowed for commendable action. Punishment should be bestowed for malignant action.
In pre-natal conditions, nobody exists apart from those who have already been born.
Therefore, no action could have been done by those who do not exist, because action requires existence.
Therefore, there are no actions that are worthy of praise or punishment from possible people.
Therefore, the answer to the question: "What did I do to deserve this [life]?" is quite simply nothing.
You did nothing to deserve the initial pleasures of existence, and you did nothing to deserve the initial pains of existence. You cannot take credit for any accomplishments before you were born, and you cannot take blame for any disasters. You did nothing to deserve to be born, for in fact you did not exist previously to have been responsible for anything. And yet here you are with your various benefits (rewards) and harms (punishments).
From this it can be argued that all births are a violation of the concept of justice and fairness. An innocent person should not be punished, and an inactive person should not be rewarded. Possible people are both innocent and inactive and therefore should neither be punished nor rewarded. Therefore they should not be birthed, for there is no reason to.
If we are to be consistent with our application of justice and fairness then we shouldn't exclude the very initial act of creating people who will be susceptible to these concepts from their domain.
Buddhism and Hinduism teach the concept of karma and the various re-birth/reincarnation doctrines, and even though I do not accept these metaphysical doctrines (apart from Buddhist non-reincarnation re-birth), I see it as a useful example of my argument. The past lives dictate the future lives. What was done in the past dictates what will happen in the future, based on the cosmic justice principle of karma. You quite literally deserve the caste you are in, according to Hinduism (a useful method of controlling the masses - a guilt-trip involving un-falsifiable historic events).
In the end, I don't know if this argument holds water or is even an argument that we ought to use to argue antinatalism, even if it is valid. It seems to kind of miss the point, or the underlying motivation of antinatalism - that of the material observation of the human condition. But it caught my attention as a potential alternative route to arrive to the same conclusion.