Nobody says you do. In fact, I agree that a lot of the paths people who have never mentored a programmer their entire life think you have to take are bullshit. (Teaching is not mentoring. Mentoring is mentoring).

However, that doesn't mean that it doesn't take a lot to become a decent programmer. It does. And not just in terms of time, but perhaps most importantly in terms of intellectual maturity.

Nobody said an Ivy League educations is (or should be) a requirement to write code. That said without some form of guidance a fledgling developer has no way to discern good code from bad or grasp the architectural or security implications of some random-ass code snippet they lifted off of SO. So again, unless your plan is to spend the bulk of your career repeating other people's mistakes in an effort to learn the hard way getting some kind of formal training should be a primary goal. I'm entirely self-taught and let me tell you from experience rediscovering a design pattern from first principles years after the book was published isn't as heroic as it sounds.