My family and I have been in the process of moving, a little at a time, for the past couple weeks, so I’m afraid life has been rather hectic around here. But better late than never.
What I recommend you do is re-post this question to our new discussion forum on Austrian economics and invite Prof. Herbener’s response. Rothbard discusses “underconsumptionism” a bit in the opening section of America’s Great Depression. There are many avenues from which to attack it, one of them being Bharat’s argument, another being the empirical case: if “underconsumption” is the cause, why did consumer-goods industries do considerably better in the crash than producer-goods industries? In my lecture on this I give some of the statistics.