Hoarding is not a problem. The word merely means saving. Saving is virtuous, not a problem to be "solved". I'm not interested in what "mainstream" economists take, give or do. If you want what they are selling, then please just stick with dollars or the local currency of your choosing, and leave us bitcoiners alone.
I agree, but I'll play devil's advocate and say that then they'll mention the free rider problem.
They'll say that since spending is necessary for a healthy economy, by refusing to spend your savings you benefit from a healthy economy generated by others, but you don't contribute to it.
The free rider problem is the magic argument to defend any socialist/Statist view of the world, anyway.
There was a nice rebuttal of the free rider argument somewhere on this forum I think, which was titled "I am a free rider" or something. The guy was mentioning all the things he selfishly uses all the time without paying one cent for it: Wikipedia, free software, scientific knowledge, public domain art and so on.