I'd rather see "ROE": Return on Expectations. A college degree can do far more than bring about a higher income. It can open up new avocations, vocations, occupations, and/or careers. It can expose you to new ideas and different ways of thinking. It can align you with the future you want. Or not. YMMV. Checking in with graduates after some period of time to see if their college degrees brought about the kind(s) of happiness they sought (and even some they did not anticipate) might be a better measure.
I agree with Rich. A seasoned welder can earn more than an MSW with a license and a few years of experience. So if your objective is to make as much money as possible as quickly as possible then that welder might earn more over the course of his or her career than the MSW especially considering that the welder will begin earning sooner and have no debt incurred upon entering the industry. But if you really want to be a social worker then your satisfaction will come from being a social worker not the paycheck. I could make more money if I went to Alaska and worked in an oil field than I likely will make in HR. But I like working in HR. Salary can play into job satisfaction for sure. But it isn't the only component.
One difference that is not commonly discussed is that the job of a welder is frequently quite demanding physically and many welders break down over the years. Work in cold weather, breathing smoke/fumes, carrying steel here and there, there are not a lot of welders over a certain age. Social Workers, I imagine, can find their way behind a desk somewhere as they get older.
For some really modern, innovative, and useful thinking around motivation and engagement in the workplace, I highly recommend Dan Pink's Drive! The research he discusses clearly points to intrinsic (as opposed to extrinsic) motivating factors. It's a good lesson for anyone in a supervisory role, or anyone working with an organization's compensation and rewards system.
I don't think there is anything wrong with looking at ROI when it comes to choosing colleges. When it comes to picking a major, it's more complicated. A lot of people are going into nursing now for the money, but I predict that many of them are going to burn out quickly. The assumption is often made that people don't choose higher-paying STEM or business fields because they're lazy or don't have the aptitude. I think most people study what they enjoy. I also think people can investigate alternatives within the scope of their interests. For example, Texas will pay up to $80,000 of LPCs' student loan debt, but only $40,000 of social workers' student loan debt. LPCs also have a broader scope of practice than LMSWs, and it takes years to work up to being an LCSW.
As others have pointed out ymmv (Thanks Rich). Yes a welder can earn a lot, a welder with a college degree is now an office based bider at a large company. A plumber can earn a very good wage, it takes 4 years of hard apprentiship to get licensed but it pays well. Now a plumber with a college degree is now dispatch supervisior at a mid to large company. An education can help just about everyone. Now a person from the hood with a degree from Everest? Is that going to help him het ahead? No I don't think so, but it might.
It matters of course. Time and cost are big reasons why I've declined certain majors/routes (like going to medical school). But each one of us has different motivations, and methods in reaching our goals.