While one more life created certainly won't do much to the total suffering of the world relatively, it not only does a lot to the person being created (making them go through grief, anguish, fear etc. in the normal course of a life), but also cannot follow from human morality. Humans do not instinctively feel it is right to do harm. And therefore a variety of things, unless cancelling occurs (right to live cancels not harming an attacker for example), since they are wrong from the start, do not end up becoming right.
This is the same thing as having a child essentially. The wrong act of creating the child, even if it leads to good things, like say ending world hunger, is still a wrong act. It's still something, if you're following your morality, you should not do. Why is having a child wrong? Because you are causing another human being to suffer. That is something that is intuitively morally wrong. How are they being caused to suffer? Every human life goes through suffering, and so too shall this one. Was it actually caused by the parents of the individual, or was it out of their hands? It was caused by them, because without the child being born none of the suffering would have occurred.
I can't make this post longer without changing the topic, so I'll keep it short.