Robert Reich lists 7 myths of economics. None of them are actual myths. Actually, he's worse than that: he calls them lies. Basically the same as a myth but without the quaintness that comes with gods having sex with animals.
If you're calling something a myth (or a lie), you're saying "this is completely wrong and people who know what they're talking about know this is wrong." There should be a lot of wide-spread agreement that the proposed myth is wrong.
For example, all toxicologists agree that it's the dose--not the substance--which makes the poison. Tiny amounts of radiation won't hurt you at all. But drink too much water and you'll stomach will explode. Too much salt is bad for you, but you need a little salt to keep your body functioning.
Actual myths are simple, so simple they completely miss basic lessons of whatever disciple they pertain to. There's a mountain of evidence demonstrating why these myths are wrong. Anyone familiar with how the discipline works knows about the evidence.
Let's look at each of his proposed myths:
1. Tax cuts for the rich trickle down to everyone else. He points to how the median wage is flat over Reagan and dropped since W. Bush. Setting aside the fact that Reagan raised a lot of taxes, simply comparing median incomes doesn't account for income mobility. If you're getting wealthier as new people enter the labor market (young people, immigrants), median income might fall. (See here, unfortunately also claiming to be dispelling myths.)
2. Higher taxes on the rich would hurt the economy and slow job growth. Reich points to historical evidence of high tax rates and high growth but this is sloppy. The question is not is it possible to have high taxes with high growth but will higher taxes reduce growth? Unless Reich wants to overturn the law of supply, the answer, at least on the margin, has to be "yes."
3. Shrinking government generates more jobs. Reich points out that government is an employer. And if the goal was jobs, that would be fine. But for economists, the goal isn't jobs; the goal is efficiency. And due to knowledge and incentive problems, more government generally means less efficiency.
4. Cutting the budget deficit now is more important than boosting the economy. I am sympathetic to this view. If we were at full employment, our budget problems would probably be solved. Not only would expenses go down, revenues would increase. It is not clear how we get to boosting the economy, however, but, in general, cutting government at least makes us more efficient.
5. Medicare and Medicaid are the major drivers of budget deficits. Reich blames rising health care costs, which supports the "lie" rather than contradicts it.
6. Social Security is a Ponzi scheme. Yeah, I wouldn't call it a Ponzi scheme, as those are inherently unsustainable, but it's certainly close to it due to demographics. And if it wasn't it's still quite wasteful due to perverse incentives and the opportunity cost of investment.
7. It’s unfair that lower-income Americans don’t pay income tax. I agree with Riech here, especially given the regressive taxes (tolls, fines, sales taxes, fees, etc). But "fairness" is a normative point. How can that be a lie? Normative is about opinion!