I think that an artist should go to art school to expand their knowledge on art but it should not be mandatory for them. A school that is dedicated to art helps artists by going more in-depth much like a businessman would attend a business school because it would teach him more in depth the different aspects of running a business. This is no different. It may be more costly, but in the end the pros far outweigh the cons and the schooling can more than pay for itself should the person pursue art as a career.
I don't believe that an artist should be excluded from jobs because they did not attend art school, but I do think it is in the best interest of the arts to have well rounded and full educated artists. And although art is thought of to be completely free form, there is a lot that artists can learn from being exposed to varying techniques and art history. Attending art school affords them knowledge and exposure to the artistic world that they might not receive otherwise, hopefully creating a better artist in the process.
An artist should be a free spirit. They should be able to create anything from their heart and it should flow from within. Art can't be made. It can be enhanced through lessons, but true art can not be taught. Anyone can draw a landscape, but a true artists sees it in their mind.
With a wide range of online classes, community classes, and other classes outside of college, improving your art skills does not require a college.
Art is not something that you learn, but instead it is something that is inside your mind and heart.
Art is not a profession that requires or benefits from a college degree, unlike genetic engineering, for example.
I don't think that there is anything that can be taught in an art school that will make an artist better at their craft. The truth of the matter is, being an artist and producing art is a very individual thing, and no amount of schooling is going to make someone better at it.
While you can learn much from an art school education, there is a great deal of expense involved in gaining that education. An art degree will not make you an "artist," and that degree will not be a selling point in the art market. If you can afford it, then it might be worth the time and money for you.