Or do they whet the appetite for more purchases and increase engagement?
many shades of grey, depending on where you are standing.
"hurt the industry" refers to manufacturers. cheap selling certainly hurts manufacturers since it makes selling that product less attractive for sellers. and one thing is for sure, cheap sellers are putzes that are not capable of increasing sales to somehow connect the dots. so they are strictly short term....or maybe have little or no commitment or investment so cannot be relied on for anything.
"hurt the hobby" is a different question. does cheap selling harm end users? probably, since manufacturers are generally harmed, therefore less creative energy gets invested in the long run. while low prices might increase a dealer's short term market share, actually increasing overall sales of hifi gear due to 'good deals' is a stretch. too many ways to view that and varied buyer motivations.
the 800 pound gorilla in the room is that high end audio is very cyclical in it's ups and downs. if the business model is too fragile and there is no profit, then everyone loses every time there is a downturn. company fails, customers left holding the bag. that great deal becomes a door stop.
after my own 50 years in retail, i do realize that customers are going to want to get a 'good deal' and
mostly don't care about a retailer's problems. but if i don't protect the business then i cannot be there later to take care of the customer and keep my promises.