While there is disagreement as to what constitutes an unacceptable life - a life not worth getting - there can be no doubt that many people with unacceptable lives currently exist. And, Utopian post-human fantasies aside, at least some unacceptable lives are a guaranteed result of the continuation of our species.
Forms of utilitarianism such as prioritarianism push us to be most concerned with the welfare of the least well off within the relevant population. But I argue that it is the very special group at the bottom, those with unacceptable lives, who are especially entitled to our highest consideration.
Those with unacceptable lives suffer a double violation. First, they are violated by being brought into existence. Their lives are worse than having no life at all, so being born makes them worse off.
Second, they suffer a new and continuing violation by being prevented from improving their circumstances in particular ways. Just as their birth is required to enable those with unacceptable lives to exist (because each birth risks the creation of unacceptable lives), their exploitation is also required for those very acceptable lives to remain acceptable.
For instance, if those with unacceptable lives were not coerced into acting in the interests of those with acceptable lives, the most miserable could either end their lives or increase their welfare toward acceptability. However, by doing so, they would likely depress the welfare of those around them with acceptable lives.
The (philanthropic) antinatalist objection to breeding is not limited, in practical application, to the decision to create a being. It also implies that those who are born with unacceptable lives, having been once violated, are entitled to special consideration once they come into existence - the "social contract" justifications for coercive policies are not applicable to them.
So these people with unacceptable lives have a strong moral claim to be allowed to commit suicide, to use mind-altering chemicals or technology, to "shirk" the "responsibilities" that the majority would benefit from imposing upon them, perhaps even to join a criminal gang. There is much less justification for coercing them into acting in accord with the best interests of the majority, because there can be no reciprocation.