Lets say the internet isn't around yet, and people still use the yellow pages. One day, they decide to charge a 10% tax on all the revenue of a business, if the

Lets say the internet isn't around yet, and people still use the yellow pages. One day, they decide to charge a 10% tax on all the revenue of a business, if they want to keep their listing in the yellow pages. Those that don't pay, get delisted. There is a competing service, the blue pages, that charges only a few cents for a listing. But it has far fewer readers, so any business that has only a blue page listing, not a yellow one, will see their income drop disastrously. So they are stuck paying a heavy tax to the yellow pages, even though if the yellow pages were to completely disappear, all the readers would switch to blue pages, and everyone would get the same search/aggregation service, for a fraction of the cost. That's pretty much the situation with Yelp/GrubHub, and I think that qualifies them as parasites (or rent-seekers, if you prefer).