It is not possible to answer this question in a way that will be correct for all individuals in all places and times. A college education can be a good investment, but it really depends on what else is available to the person.
When a person goes to college, they give up the possibility of earnings in the present. In fact, they generally have to expend a great deal of money to go to college. So, for the four years or more that they are in college, they are losing money instead of making it. In order for college to be a good investment in monetary terms, they need to be able to make up for this loss of money in the long term.
So, a college education is good in the long term if it allows you to make more money in total than you would have if you had started to work after high school. For many people, this is true because college allows them to get a much higher-paying job. It also tends to allow them to get a job that is less likely to be lost to mechanization or offshoring. Therefore, a college education is often a good investment in monetary terms at least.