Why do so many companies require a college degree for employment?

It was not that long ago that relatively few people graduated from college and a high school degree was all you needed to get hired. With regard to getting a job, a college degree now is equivalent to what a high school diploma used to be. Some are suggesting that free education should be extended to the college level. Given the business situation and the high cost of tuition, this seems like a reasonable thing to do.

I loved going to college, but I can’t say that I make much use of what I learned there. I work as a computer programmer and all the programming I know was learned on the job or on my own. I can see how some areas like engineering require special training, but why should a degree in the humanities make a difference? There are no specific course requirements for getting into law school or medical school. Why not go directly from high school into these schools?

I have seen the opinion given that college is like an obstacle course, demonstrating self-discipline. Do you think that is true? If so, is that a reasonable and fair thing to do?