>>61>>63Autodidactism of a full discipline starting from a certain starting point (e.g. a minimum math level and minimum complex comprehension level and problem reasoning level) is good when you have no time limit to do your studies: your time is open ended and your studies can go on indefinitely.
This is not so when you want to achieve a certain level within a defined timeframe. Why is this? You don't know what you don't know. Let's say you get some advice about specific topics to study and perhaps you'll buy the same textbooks that a college degree would prescribe. Now you have to study it. Since you are untrained, you're going to have to pick up EVERY LITTLE DETAIL before you can decide "this bit of knowledge is more important for my progression than this other bit of knowledge". This would take significant time and effort, even more than you'd be doing with a structured education course. You probably don't have peers to discuss your studies with and special purpose Internet forums aren't always the best way to clarify what needs clarification. Even if you finish all the textbooks you've got, how much knowledge do you need before you get to "a good amount of knowledge"? Once again, you don't know what you don't know. This is fine if you've got all the time in the world to build all the knowledge you want.
Structured education is different to this. In all forms of structured education that I've encountered, there have always been unit outlines that describe the learning outcome that one is supposed to achieve for the unit; there are always adequate challenges that further reinforces the theory that's been taught; there are also teaching staff to provide instant feedback and advice about the learning materials. Lecturers will lecture about the absolute basic ideas about the study unit and may also find ways to relate it to reality - progress is well defined and the fundamental knowledge about the subject is defined as well giving students a context about what to study specifically. There are also classmates who would be in a comparable study level to yourself so you can do group study sessions with everyone being on the same page.
Resources like Khan Academy are fantastic because its course structure, education materials and mode of development that is suitable for autodidacts and teachers alike. The thought of completing the level of training in Khan Academy with nothing but a bunch of books and a lot of time is something that the vast majority would not do on their own accord. I guarantee it. You are shitting on people who are capable of learning but don't want to go through the uncertainty of "I don't know what I don't so what should I do".