No one can make a rational argument that simply stuffing money under a mattress has a positive effect on the economy or increases future wealth in any way, it is instead a tax on productivity and this has been know for centuries. Investment CAN be productive and every reasonable person can see how it generates real returns and increased wealth, but mattress stuffers can not claim those benefits as being caused by their actions. BitCoins economy is pure mattress stuffing without a hint of productive investment (no before you ask buying an ASIC with BTCs is not a productive investment), and the nature of the coin guarantees it always will be hoarded, that is the flaw in deflationary economics.
Bullshit.
The mattress stuffer first had to get the cash before they could hoard it. If they can't just print it out of thin air it means they actually had to go out in the world and trade for it, by producing valuable products and services. In order to still have the cash, it means they didn't spend it, which means they have consumed less than they produced. This is where the economic benefits of saving come from. The savers are investing, by adding their productivity to the economy while simultaneously limiting their consumption.
The harmful effects of hoarding that you're thinking of are when banksters and politicians just type new balances into their own bank accounts and spend without ever having to contribute any value in return. You're trying to blame deflation for the harmful effects caused by inflation.
Mining bitcoins isn't the same as saving as described above, but unlike government money inflation it is voluntary, limited, and transparent. It will become increasingly insignificant over time anyway so it's not relevant to a long term analysis.