I am an assistant professor of economics and am, therefore, untenured. I go up for tenure after next year. Stephen Karlson at Cold Spring Shops has these thoughts on the tenure system.
Getting the chance at tenure is one of the benefits of the job. Generally speaking, assistant professors are willing to take a lower rate of pay to have the chance at tenure. If tenure were abolished, many would likely move out of academia if they were not compensated with a higher salary. I imagine this is especially true of professors from disciplines that are well-represented in the private sector (economics, finance, engineering, chemistry, medicine, etc.)
But the chance at tenure is not the only reason to work in academia. During the school year, I often do school-related work 7 days during the week. But other than my teaching schedule and my office hours, my work schedule is very flexible.
I also teach 8 months a year and have my summers off from teaching - if I so choose. I have the opportunity to teach summer school, but at this point in my career, I prefer to take the summer off to concentrate on my research. I have about 25 years ahead of me in my career. Research is something that doesn't pay off much in the short run, but, instead, generates long-term benefits. So I view today's research as an investment in my future.
I also teach a 4-4 load which gives me relatively little time to start up new research projects during the semester.