I would point out that it is impossible to be born as any person other than the one that you are. If in an alternate reality one or both of your parents had children with someone else, none of those people would be you. If you believe in “pre-incarnate” souls, then it’s possible that in those different realities the same soul would be born to someone somewhere, but they’d have a very different life with a different meat-brain which comes with some hardwired and “softwired” personality traits. There’s no meaningful way to say that they’re the same person - at the very least, they’d almost never be recognized as such. In the case of “did not consent to be mixed-race” even if that really mattered, such a person could never exist as anything other than a mixed-race person with the same parents that they already have.
(That really sucks for people for whom some aspect of what they are causes them legitimate misery, for example a trans person could never have been born with the right kind of body, but that’s sadly how it is.)
And then the whole “consent to being born” thing is in general rather stupid because in order to consent to something, you first have to exist. And to meaningfully consent to something, you have to fully understand the implications and consequences of your choices. A non-existent person cannot do that. A baby cannot do that. A young child may be able to consent to some things, but they cannot meaningfully consent to something of that magnitude. After a certain level of general knowledge and maturity one can technically consent or not consent to existence, though that gets into the thorny ethics of suicide. But unless one can exist as an adult with an age in a negative number of years, “consent to being born” is an inherently meaningless concept.
But, let’s be generous and assume what they actually meant was that it’s not moral/ethical to have children unless you can and do give them the best care possible. That’s a rather modern view, limited to highly industrialized societies, because such a thing is/was otherwise not even remotely possible for anyone other than a privileged few. Until very recently, employment has been actively hostile to parenting, and it’s still a serious problem in some countries. If nearly everyone stopped having kids, their society would crash within a generation. Maybe fix things first before shaming people? It’s not like the average poor person can overcome structural inequalities with sheer force of will. That would mean developing psychic powers and mindraping everyone, and you don’t want that. :-p