There was NOBODY there of whom it could be said that she/he was forced into existence – and thus harmed – when future parents procreated and a new human began to exist.
Once the new human exists, though, we are entitled to say that the human being in question didn’t have the liberty (and couldn’t have had the liberty) to refuse the beginning of its existence. Persons can accept their existence when it would be too late to reject it. They can only reject their existence when it’s too late. This is where antinatalism comes into play as a kind of paternalistic moral theory. Among other things antinatalism takes very serious the chance – and enlightens about the fact – that a new person might reject her very existence.