[Hacker News Comment]
But you do study Philosophy, Medicine, Economics, Archaeology and Anthropology and many other subjects without having studied them before. The subjects that are not (or are rarely, or badly) taught at school often expect people with little existing knowledge but a strong interest and an enquiring mind. Computer Science falls into this category. Also if you think of Computer Science as being primarily about programming rather than the maths, theory and science of computing I don't think you fully understand computer science.
I chose to do Computer Science because I wanted to properly understand computers. I had essentially no programming experience although I had tried a couple of times but hadn't found the right way in, (QBasic by Example didn't work for me and I didn't discover K&R or a C compiler which I think would have worked better for me). At the end of my degree I was definitely not a great programmer but I could program in Java and ML (taught in the degree programme) and C/C++ and the WIN32 APIs self taught and used for my final year (significant scale but poorly structured) project.
There people on the course (at a very famous university) who really couldn't program at the end of the course but knew the material and official answers well enough to get good degrees. There were also many that started with good programming skills but it was certainly possible to learn enough in the three years to be able to start work and do useful programming and build experience.
Something that surprised and disappointed me at University was how few people seemed to really try to take advantage of being there and learn generally within and beyond their subject rather than being course and exam focused (not just CompSci but all subjects).
Am I a great programmer? No, but I've only spent 15 months within a professional development team, another couple of years on demo level and proof of concept software in an R&D environment and the last year self retraining in iOS and Rails development following five and half years in Product Planning and Business Development.
Who should you hire? I don't know but some simple programming tasks I. The interview stages are probably a good idea. If you want someone who is just a programmer maybe someone incurious is a good bet if they have the skills you need now but whether they are self taught or university educated I think the big question is whether you want someone to fill a particular role now or for the future growth potential that they have. If you are only interested in the fully capable now rather than the trainable (and mouldable to your company way) you may miss out onbetter long term bets.