I understand that, hoarding causes deflation. But as said in my example, deflation devalues real capital and that doesn't encourage investments.
The thing you fail to see is that money is a common. You're holding it now, but it belongs to the whole society because it is an abstract good, an agreement. The money you hold could be worth nothing overnight if society decides so.
So the way people saves should be the way that the society benefits more, and that's not hoarding.