A full employment U.S. economy would be nearly impossible to reach. I think we could get within a percent or two, but zero unemployment would be an unrealistic goal. In theory, if every person in the U.S. who could work was working, the economy would be stronger. The government would not have to pay unemployment benefits to anyone, welfare payouts would be low or non-existent, and businesses would be thriving because they would be fully staffed.
Currently the unemployment rate is dropping, and has been dropping for several years, as a result of an upturn in the economy after the recession in 2008. If the U.S. continues to promote policies that encourage people to work, we will continue to see unemployment numbers decrease.