Many young progressives think they have found a fail-safe way to end poverty: a universal basic income (UBI). The idea is very simple, they say: Every month, the government cuts a check to everyone. Period. That way, no one has to fall below the poverty line.

The UBI is an old idea, which also has a storied history on the right. Many conservatives like the idea of a simple welfare system that would replace arcane programs and nosy bureaucracies.

And indeed, right-winger that I am, I was for a very long time a strong proponent of a UBI. But now I oppose it.

What happened? I looked at the best science and changed my mind.

Here I must make a slight detour into epistemology. Most social "science" research is actually not science, technically speaking. Science, properly understood, is the testing of hypotheses through rigorous experimentation. This is not what most published social science studies do. Most published social science studies rely on modeling and statistical analysis to try to formulate theories as to what is going on. Most studies are really elaborate thought experiments that, until they are or can be validated by experiment, are not scientific results, properly speaking. To be clear, it doesn't mean this academic work is valueless. There is great value in theoretical work and, in some areas, that's all we're ever going to get. But most published social science studies — as we all know deep down — actually do not prove anything, which is why you can probably find enough studies to back all sides of any issue.

There is, however, one way to gain relatively reliable social-scientific evidence: randomized field trials (RFTs). Because they use a randomized control group, these experiments actually have a fair shot at robustly demonstrating cause-and-effect relationships, especially if the experiment is replicated many times.

For example, we know that people who go to college make more money on average than those who don't. But what's the cause-and-effect relationship? Is it that college makes people more likely to succeed, or is it that people who are more likely to succeed attend college? The only way to get a reliable scientific answer would be to take many random groups of people, over a long period of time, and put some groups through college and others not. That is the only way of even having a shot at scientifically ascertaining the cause-and-effect relationship.

Obviously, we don't do that. And that doesn't mean studies on the college wage premium are valueless, or that we shouldn't form an educated opinion from social science studies. But as we do so, we should be aware that these studies do not rise to the level of scientific evidence, properly speaking. Only repeated RFTs do.

Unfortunately, RFTs are very rarely used. There are very few domains of social science where there have been any RFTs, let alone enough repeated RFTs to get a reliable result.

What does that have to do with the UBI? Well, it just so happens that the UBI is one of the very few, if not the only, domains of social science policy where we have exactly that: extensive, long-term, repeated RFTs, which are the gold standard of evidence in social science.

As RFT expert Jim Manzi writes, these experiments "tested a wide variety of program variants among the urban and rural poor, in better and worse macroeconomic periods, and in geographies from New Jersey to Seattle"; more than 30 experiments were done in the U.S. from the '60s to the '90s and there was another set of experiments done in Canada in the '90s. The universal basic income is one of the few areas of social policy where we can say with some confidence "Science says..."

And science says the UBI doesn't work.

As Manzi writes, one of the few consistent findings across all these experiments is simply this: The only type of welfare policy that reliably gets people who can work into work is a welfare policy with work requirements. All the evidence strongly suggests that if you have a UBI, the outcome is exactly what many conservatives fear will happen: Millions of people who could work won't, just listing away in socially destructive idleness (with the consequences of this lost productivity reverberating throughout the society in lower growth and, probably, lower employment, in a UBI-enabled vicious cycle).

This is not a minor concern. As Megan McArdle has noted, the latest research suggests that work is a central part of human flourishing. Long-term unemployment is worse for self-reported well-being than divorce or the death of a spouse.

The evidence overwhelmingly suggests that getting as many people as possible into the workforce is a highly laudable goal. A welfare policy with work requirements is the only realistic way of accomplishing this goal. And a UBI would consign millions and millions of people to deep misery. Writing as a former strong proponent of UBI, and having given a long hard look at the evidence, I must admit, this was a true revelation. It's now impossible for me to support a UBI.

Now, of course, there are ways to dispute the evidence, and the conclusion.

Most of the welfare RFTs were done decades ago. Perhaps, post–Great Recession, the situation would be different, and the implementation of a UBI would turn out differently. And there are value judgments at play. There is a deep strain of left-wing thought that views work as inherently alienating, and perhaps "freeing" people from having to work would ultimately result in human flourishing, whatever the costs. For reasons that should be obvious, I don't view these arguments as remotely convincing.

But what's striking about this whole debate is to see young progressives, who very much fancy themselves the party of science and reason and empirical thinking, not even dispute or wrestle with, but in fact just utterly, completely ignore the actual scientific evidence, and this in precisely one of the few fields where we do have reliable evidence.

For my part, I did look at the evidence, and my mind is made.