I think the key here is that these deal sites take most of the money - that's not sustainable or profitable for the sites' customers (restaurants, shops etc). They're being greedy and will pay for it with the hostility of businesses and eventually death as the deals dry up.
If they took less money, and were less agressive in driving prices down, businesses could price deals correctly so that they're not making a loss on each new sale and the deals benefit everyone (site, businesses, customers).
If they took less money, and were less agressive in driving prices down, businesses could price deals correctly so that they're not making a loss on each new sale and the deals benefit everyone (site, businesses, customers).