And that's, I think, a good display of the issues underlying that kind of saying.
Parenthood is being put up as such a monumental task, with impossible standards, that it makes the careful and reasonable cancel or delay any project of parenthood, while not likely having any impact on the careless who are to become the kind of parents the sentiment was meant to critique in the first place.
People have been parenting since the dawn of time, before the existence of any education or economic system. They certainly haven't all been /good/ parents, but I do feel that there's this mainstream discourse that needlessly discourages people from becoming parents. I mean, sure, there are some local exceptions, and I don't want to go into politics because I've already gotten a warning about expressing my thoughts about places not having paid parental leave or any kind of parental job protection. But other than for those places, I really don't see any reason that parenthood should be delayed forever further and further into one's life. Can't not think of Idiocracy's intro about this.
We had our first kid relatively young, by today's standards (not by previous generations'). Hadn't finished our studies yet, but it was planned, and we finished them with the baby without any significant problem. Not for everyone, though, I'll grant that. But waiting off until your whole life is set and you are 100% confident that you'll be a superparent before having your first kid, somewhere in your thirties at best? I don't think that's good for society. I don't think that's healthy.
"Perfect" shouldn't stand in the way of "good". "Perfect is the enemy of good", it is said. In my opinion, parenting is firstly a matter of will. It's not about having all the innate qualities and answers to all the problems. It's about the will to persevere and do what's best for your kids. As such, all this fear about being ready is a red herring. You can't prepare yourself to parenthood. You just have to want it.