"Every dollar they receive (and a lot they don't) gets invested in the economy in some way (salary, materials purchases, R&D, etc.)"

Two problems with that statement. First, you're only looking at one side of the equation. You're ignoring the cost and damage to the economy that government spending does. I don't just mean by crowding out other, more efficient solutions, but the literal taxation and inflation that government uses to get the money in the first place inhibits economic growth. Both actions reduce the "bottom line" for consumers and companies and thus reduce the funds they have available when deciding to make capital purchases- whether it is a house or a car or sending kids to college or building a plant to create more jobs. All of the money government takes prevents those things from happening.

The second is that you're ignoring that much of that "investment" is actually spent on activities that are themselves net-harmful to the economy. Such as the overzealous regulators that shut businesses down, the agencies that spend their time inhibiting efficient running of businesses, or even make it impossible to operate your plant safely because government regulations don't allow the use of the latest safety equipment (only what was on the market at the time the regulation was created) or FDA examiners that drive costs thru the roof, and prevent access to drugs for dying people because the drugs are "experimental" and might kill them in 20 years (though their disease will get them a lot sooner) etc. Much of the money government spends is on programs that make people less safe and more on topic, undermine economic growth with no real benefit other than providing good political jobs to hand out.

"This is a lovely dream with little evidence to support it."

The entire history of the USA supports it.

"The idea that rich people getting richer helps the economy is not founded on fact."

The error you're making here is that you think that letting people keep their money only helps the rich. IF you take all of the incomes of the bottom %50 of the populace and you compare it to the incomes of the tope %50 of the populace, there are a lot more people in the lower half and they make a lot more money. Not squandering that money benefits them a whole lot more than it does the rich.

Frankly, the economics are not really up for debate. They don't support your side. The slogans about "rich people getting rich" are just rationalizations for theft.

That theft, actually, hurts poor people more than it does rich people. Rich people are insulated, the poor are not.

Bush's original Tax cut proposed reducing taxes for poor people by %50, IIRC, and the reduction for the richest was around %2. After the democrats managed to "compromise" it, what got passed reduced taxes for the poorest by %20. Why weren't the democrats in favor of the large tax cut for the poor?

And even still, even though every way you measure it-- dollar terms or percentage terms-- these tax cuts helped the poor more than the rich, ever since they've been passed, democrats have been calling them "tax cuts for the rich".

Frankly, from an economics perspective, lower regulation, lower taxes, lower inflation, no matter how unevenly applied, helps the poor. It always does, it always will, and in fact it has to-- the primary way you get rich is by improving the lives of the poor.

I don't understand why democrats constantly support policies that hurt the poor, are constantly trying to raise their taxes (While always, of course, claiming to only want to tax the rich) but they do.

I'm not a republican, so, put down that assumption I've just studied economics. What the politicians tell you about economics is designed to serve their interests, not yours.