No doubt, it is sad for your friendly neighborhood restaurant to go out of business, but at the end of the day it is every owner / manager's responsibility to understand and own up to their pricing and discounting decisions. Of course if you'd offer to give up a dollar for a quarter (exact economics of a Groupon deal) you'll get swamped with takers and get ruined.

Groupon salesforce surely sold them stories on how great it is, but at the end of the day there is no excuse for not doing your own math. I suspect many "Groupon drove me out of business" stories are simply a way to blame someone for the overall business failure. Might as well say "it is due to economy" or "changing neighborhood demographics" or "to spend more time with family" or really anything.

EDIT: When I say "blame" I mean anything listed as a "reason". People often like to be indirect when they do the blaming.