The question of whether or not a university degree is needed comes up here quite often. In some parts of the world, it’s becoming increasingly necessary. But that question is different from whether or not it’s possible to learn graphic design outside a college or university.
I think it’s possible to do so, but more difficult. When given the choice, people have a tendency to focus on those things they like the most or can do best. In a good, formal design curriculum, students are exposed to most of the basics and required to work hardest on those things they might be least adept at doing. After graduation, there shouldn’t be many gaps in basic knowledge, and there should be a good understanding of what one is capable of doing. In other words, a good foundation has been laid.
Although it’s becoming increasingly more difficult, I think it’s possible to form this same foundation on the job if one is fortunate enough to get a job at the right place with the right mentors who are willing to hire someone with little to no experience. Most business won’t do that anymore since it’s more cost-efficient to hire from the glut of college-trained designers who already know the ropes. I suppose it’s possible — even without a formal education — through a series of non-skilled jobs, for a focused beginning designer to move up through the ranks to better jobs while picking up more knowledge and experience. Even so, that person will soon run into the prejudice of employers requiring degrees.
As for teaching oneself, on one’s own, through online tutorials and books, I’m not at all sure it’s possible given the lack of feedback, critiques and direction from more experienced and knowledgable designers. Lots of people have taught themselves how to design logos or learned how to successfully navigate crowd sourcing sites or become proficient at various kinds of software. Sometimes these people get very good at those tasks, but there are still giant, gaping holes in their knowledge due to things they’ve never encountered or had a need to learn about.
With the mix of more experienced designers and newbies, I think forums like this one can fill in some of the gaps for some people. It’s no substitute for school and the critiques that happen there, but sometimes people’s misconceptions can be challenged and various ideas put out on the table that might not have been considered otherwise.