I think your advice is correct for those that want kids. The issue becomes contentious when this is advocated to people who mostly are on the other side of that decision. Going for kids before you are ready is still aligned with ‘wanting kids’.
Wanting is only a part of the equation. You need to both be willing and able to be a competent parent. Some people lack the emotional stability required, for example. Others don't tend to see such long-term projects to completion, abandoning their hobbies even a few years in. Yet others just don't have the resources, unfortunately as it is, or have other factors significantly limiting their ability to be good parents.