While all education is, at its root, self-education (no one can hit the books for you), there are not a whole lot of engineers and physicians out there that are self-taught, and I don’t think it’s just the credentialing barrier.
Even in computer programming, where the need for self-study is most evidently manifested, and there’s quite a few people in the field that are self-taught, the benefits of a quality computer science degree go well beyond getting a diploma at the end of the four years.