I disagree, they provide value by keeping premium domains available for people with money.
> Thanks to Uber you now can seamlessly hail a ride to wherever you are. Thanks to AirBnB you now have a great alternative to hotels.
Uber started as UberCab.com , AirBnB started as AirBedandBreakfast.com . Premium domain name is not required to start a successful business.
> If it wasn't for domain parkers, you'd still get your domain - just for 10$, rather than 10.000$.
Or not, it could have been claimed (possibly unused) with the owner not checking their email. I think domain parkers solve this very problem.