Unfortunately it is currently difficult to ask the unborn, so you do one of two things:
1) Rely on their prospective parents decision. To improve the parents decision making you attempt to improve their education and increase access to contraception.
2) Enforce laws about how many children a couple can have.
Most places have followed method (1). China followed method (2) (but also increased education).
Both methods seem to have resulted in dramatically better standards of living in less than a generation, and many people from drastically poor areas have gone on to live fulfilling lives.
Indeed some have accomplished more than I ever will - for example, the greatest distance runner of all time[1] grew up as 1 of 10 children of subsistence farmers during the Ethiopian 83-85 famine[2]. You can't get much deeper in poverty than that, and yet he won 2 Olympic Gold medals, 8 World Championships and broke 27 world records.
I'm unconvinced he would think he should never have been born.
Also - as the linked article shows - it is possible to tackle problems like malaria relatively easily and cheaply, if there is the will for it.
>I'm unconvinced he would think he should never have been born.
Yeah... the 1 in a million person is always the wrong person to ask. Perhaps if you asked the millions who have suffered and died if they would have been better off not ever being born, you might get a more meaningful statistic.
But you don't exactly see millions of people offing themselves, so clearly the human spirit survives such adverse conditions?