This is a green heron since the issue at hand isn't "oh but you can study without a diploma", the issue is "you won't be taken seriously because you don't have credentials" e.g. piece of paper.
The credential is that they were able to pass their classes, hopefully with good grades. Many employers want to know that you are the type of person who succeeds, not that you know some specific thing. University has basically taken the place of apprenticeships because employers don't want to train incompetent people, so they make you show competence with a degree.