How does taxation take anything out of the economy that purchasing from any other source doesn't?
Directly not. Simply like robbery. What the owner would have owned, is after this owned by the robber.
Indirectly a lot. Some people, instead of creating useful things, become robbers. Some harm is done to the things robbed. A lot of value is lost - you rob my computer, you use the computer, but my data, if of no value for you to blackmail me, will be simply thrown away, lost, even if I would value them a lot. I try to prevent this by security measures, which are costly. So, robbery creates a lot of harm. Similarly taxation, which is nothing but a form of organized robbery.
Well in the civilized world Keynesian economics isn't bullshit and is backed up with centuries of evidence....evidence you like to ignore.
Keynesian economics is the economics of corporatism, of fascism. The economics of a free society is more close to the Austrian. Ok, an oversimplification, there are valuable economists of a free society which are not Austrians, like David D. Friedman. I do not ignore Keynesianism, I reject it as false.
First, Keynesian economics has absolutely nothing to do with politics or corruption.
Yes. It completely ignores it and presents the government as a nice guy, with universal knowledge and good intentions. Instead, a reasonable economic theory would have to consider, if it does not completely reject the state, the economic laws which define how the state works. There is a whole domain, public choice theory, about this.
Oh, then how do you explain all the monopolies which existed prior and resulted in the banning of monopolies? The reason all developed economies now ban monopolies, with a few exceptions, is because they were first created and proliferated during a period in which monopolies were legal. The American Revolution came about in part because of a particular monopoly.
No, banning "monopolies" is a nice method to get campaign contributions from such "monopolies" in exchange for leaving them alone.
Perhaps you can give an example of a modern monopoly created by the state (not Russia or any of its affiliates) in which the state has created a monopoly (utilities exempted).
Go into a patent office, ask for some patent, find out who owns it, and you have a modern monopolist created by the state.
And how do you explain the rise of the 19th century robber barons?
Most of them by state subsidies. Some of them were simply good in their job. And, therefore, hated by those who were not that good.
BTW, it is well-known that the Austrian and the Keynesian position about what means inflation is different. I prefer the Austrian one, as more reasonable. Feel free to follow you beloved Nazi Keynes, I couldn't care less, but stop claiming that I do not understand inflation if I do not use the Keynesian nonsense.
Oh, so you don't remember writing, " Stuffing money into mattresses is a harmless private hobby, which does no harm at all.
Why? You don't understand the difference between something being a harmless private hobby and being a good idea?
And what goods would they invest in?
In goods which, in their own opinion, provide the best way to secure their own future, and that of their family. One buys simply a house, to live there, another one a greater house, so that he can also rent a room, some invests into some firm, which can be managed by their children later. Depends.
If there is no or little demand for goods and services there is little demand for investment.
If there is not sufficient demand, prices fall, after this there is sufficient demand. Not a problem in a free market. It is a problem in a market where the superrich have got a lot of printed money to build fabrics to create an artificial boom. Because in this case, the investments will not pay. Many of them go simply bankrupt. Big problem. (For the rich, and for the taxpayer who pays for the "too rich to fail").
Keynesians seem unable to understand that general demand is nonsense. There is more demand for X and less demand for Y. The market corrects the price relation.