Guess I should have made my definition of "sharing" more explicit:
Share: have a portion of (something) with another or others.
I never said sharing should be free. Carrier share towers (for fees), companies share office buildings, warehouses, etc.
"I would argue that the way it's traditionally understood, sharing is something that happens between equals, or people who have an intention of becoming equals."
Well, that's your definition. We can spend the rest of our lives arguing about definitions.
"From this perspective, it's obvious that CouchSurfing is sharing while AirBnB isn't: on AirBnB, the expectation is that there is a split between the seller and the buyer; on CouchSurfing, there is a shared identity of "travelers" and an expectation of reciprocity."
So, by my definitions, AirBnB is sharing, so is CouchSurfing.
"by your own definition of how you use the word sharing"
Again, you're implying a different definition of sharing than I'm using (or even that the dictionary uses).
"somebody might decide that their car is an underused asset which should be "shared""
The car yes, but you're not paying for usage of the car, you're paying for a transportation service.
"Well, so do AirBnB hosts when they clean the room after you stayed in it...)."
That's asset maintenance. Someone driving a car isn't asset maintenance, it's a service. And that's even charged separately, usually (as a "cleaning fee").
"tl;dr: Your conclusions don't actually follow from your implied definition of sharing, and your definition of sharing doesn't match the general feeling that the word evokes."
Not only you wrongly implied my definition of "sharing", which I actually took from a dictionary, but you also didn't understand the difference between usage of assets and labor services. Another way to look at it is: what's the main cost component? Is it return on assets or labor?
- Uber: labor
- TaskRabbit: labor
- AirBnB: return on asset