Okay, let’s step back and talk about what ‘Supply Side’ economics is, and how it differs from demand-side economics.
Let’s say we have an economy that is stagnating. Consumer demand is down, jobs aren’t being created, business investment is low. So what’s the right fix?
“Demand Side” economists would say that low consumer spending is causing investment to shrink. Inventories grow because no one is buying, so businesses start laying off employees. That takes more money out of the demand side, causing even more businesses to fail. The answer then is to prop up demand by giving people lots of money to spend.
‘Supply Side’ economists would say that demand is down because businesses aren’t making what people want, or the cost of business is too high. To fix that requires investment in new businesses and products. “If you build it, they will come.” So, the argument is that by removing the impediments to business, you spur innovation and the creation of new products that people want, and that stimulates demand.
If there is unemployment, a supply sider might say it’s because labor is too expensive. There’s a supply and demand curve for labor just like anything else. So minimum wage laws, regulations that make employees more expensive, overzealous worker protection laws that make hiring people too risky, and other costs of labor price many people out of the market.
So who’s right? It depends. It’s stupid to believe in ‘demand side economics’ regardless of the specifics of the economic situation, just as it’s stupid to call yourself a ‘supply sider’ regardless of the situation. Furthermore, you can believe in both things simultaneously. It all depends on context.
For example, if your capital gains rate is twice as high as your trading partner’s capital gains rate, you have a supply side problem. If you have worker protections so strong that it’s almost impossible to fire someone and as a result you have 25% structural unemployment among citizens without a solid work record, you have a supply-side problem.
On the other hand, if you have low business taxes and regulations, but a financial crisis has spooked the population and they start saving all their money, you have a demand side problem.
You can also be in a situation where you have predominantly a demand-side problem, but there may be no good solutions available. In that case, it’s worthwhile to see if there’s anything you can do on the supply side to incentivize businesses to invest and create new products that may generate demand.
Also, you can have economic problems that are simply the result of a mismatch between production and demand, either because the culture has changed, or technology has changed what people want, or because government policy or an economic bubble has distorted production to the point where people don’t want what businesses are making, or because a disaster strikes and changes the mix of things people want and need. In that case, your best plan of action may be to do nothing and let the economy adjust itself. Accept that you’re going to have a downturn until the economy can correct itself.
Supply side policies don’t have to include tax breaks. Regulatory reform to lower the regulatory cost to business is a supply-side move. Stability policies to reduce future risk can improve the supply side. These things can be done in conjunction with demand-side stimulus if necessary.
So to answer the OP’s question, no, those things don’t invalidate ‘supply side’ economics. What they might indicate is that the recession of 2001 wasn’t caused by a supply side problem. If the problem was with demand, then giving businesses tax breaks will simply cause them to save the money, since they can’t find profitable paths to expansion.
The reason I say ‘might’ is because there were many factors that changed the economy drastically in those years. The WTC attacks erased a trillion dollars in wealth, just as the U.S. was coming out of a recession. The tourism industry took a massive hit. The government was passing new regulations willy-nilly to make everyone ‘safer’. In addition, Sarbanes-Oxley was a huge regulatory kick in the teeth to smaller public enterprises, the Bush Administration was toying with protectionism, the public mood was terrible because of the fear of terrorism, and the U.S. was gearing up for war. It’s not surprising that the economy stumbled. What we don’t know was what the relative contributions of all these factors were.
One fundamental mistake in the OP is to assume that supply-side economics is just demand-side economics for rich people. It’s not. The whole idea is to get them to invest their money, not spend it. Presumably, those wealthy people who ‘saved’ their money saved it by putting into a mixture of high and low risk investments, including startup capital for new ventures, investments in their own businesses, savings that banks then loan out to other businesspeople, etc.
If you just give money to rich people so they’ll run out and buy Porsches, you’re engaging in demand-side stimulus, not supply side economics.