They’re wrong, according to a new study from the American Action Forum. Here’s report author Robert Book‘s executive summary:

Over the past year, several studies have claimed that the Affordable Care Act’s (ACA) Medicaid expansion will create new jobs and economic activity, and that states that decline the expansion are needlessly forgoing jobs and economic growth that could be obtained at no cost. These studies—ranging from a nationwide study[1] from the President’s Council of Economic Advisers (CEA), to state-specific studies from numerous interest groups and academics[2]—all use similar methodologies. They arrive at their results by ignoring necessarily offsetting factors, and thus their claims are unfounded. In this research, the American Action Forum (AAF) estimates of the impact of the Medicaid expansion on a state-by-state basis, taking into account all available offsetting factors. Expanding Medicaid may have many effects; however, we find that increased employment and economic activity are not among them. Instead we find that Medicaid expansion, if adopted by all states, would result in a direct net loss of up to $174 billion in economic growth nationwide over ten years, and would result in the loss of over 206,000 full-year-equivalent jobs for the years 2014 to 2017.

And the conclusion:

Previous studies predict large and beneficial macroeconomic effects of the ACA’s Medicaid expansion, by calculating the economic benefits to individual states of the inflow of federal dollars predicted to ensue. However, in calculating those benefits, these studies typically ignore one or more offsetting factors, most notably the taxes necessary to pay for the Medicaid expansion, the deadweight loss associated with this taxation, and even the direct loss of premium subsidies that accompany eligibility for Medicaid.

When we take these offsetting factors into account, the picture changes considerably. Instead of an increase in economic growth and jobs, we find the opposite occurs—billions of dollars of economic activity, and thousands of jobs, are lost. Some states see small net gains, but the total losses incurred in other states substantially exceed the total gains.