I should make sure to distinguish supply side economics as a whole, from the Laffer curve, which is a type of supply side theory. The Laffer curve suggests that as tax rates are lowered, government revenue will increase through economic growth, and that this will compensate for the lost revenue from the reduced rates.
The Laffer curve probably works in a society with very high rates of tax, in which people are actively demotivated by the amount of tax they pay. There's no evidence that it works at other rates.
Nor is the trickle down effect a meaningful concept.
As I've said for a long time, the place on the tax curve that I believe a government might usefully support is the part that leads to dynamic entrepreneurial activity. For me, it's shopkeepers, people with a particular expertise, kids working in garages, these sorts of people that are the furnace of wealth. So you build an environment which supports them.
Wealthy financiers are not the engine of innovation. They are one means of support for it but by no means the only one. Personally, I like it when a government defines programmes that target and help finance the people taking the risks themselves, not giving breaks to wealthy people who are apt to figure out ways to avoid paying much tax anyway.
Indeed, I suspect there's little point in giving tax cuts to the wealthiest people for the purposes of innovation anyway. They have no need to take a risk. And they tend to avoid investing at the earliest and riskiest stage of an idea. It's that stage that needs support, in my view.
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