I agree that there is something off putting about these companies in that, as a cynic, I think they are simply putting a nice whitelabel wrapper on someone else's work. That being said, it is hard to make the case that this is centralization and I have concluded that I believe these businesses are good because:

* Everyone is a private contractor, they are free to make their own choices and work (or not work) for a company.

* They can be flexible service providers and they can create their own reputation.

* Companies like airbnb/uber/sprig simply provide a platform . It is likely that many platforms will arise as for some of these businesses the barriers to entry are pretty low. The workers and producers can be on all platforms or go completely independent but Uber without driver's isn't a 50b company.

* If your options are make some money in the "sharing economy" or make no money in the "real economy" I think you would choose to hop in.

i see this as the new websearch model. Companies provide the best results and ratings, while offering ancillary support to users and charge them instead of showing adverts. the problem is if one gets really good, really powerful and effectively controls a lions share of virtually all of the search results routing all queries and related services through a single provider. lets hope that if that were to happen that not only would they not be evil but that they would good.