Watch the first 10m of idiocracy on youtube

I guess it matters what "shitty" parent means. You can give all the financial/material support in the world to a child and still cause irreversible lifelong damage with the wrong parenting style. You don't need to be a "perfect" parent, but at the same time you do need to be a "good enough" parent, or the consequences are dire.

Knowing what I've been through, I'd much, much rather those people spend an extra 5 or more years working through those problems instead of having children that will grow up to regret being born.

And reality is, some people should never become parents, because they carry mental issues they will forever lack the self-perception to acknowledge and attempt to change. But they will become parents anyway, and the outcome is all but certain.