Contractors for low skill work is exclusively a means to avoid the overhead of having an employee and all the worker protections that entails. The "contractor" has no negotiating power, and no protections normally given to employees. For the Uber "contractors" it's the worst of both worlds while Uber get to have their cake and eat it too.
They want to terminate/not renew your contract because they didn't like you for some reason ? They can. With no extra fee to pay. So imagine if they find out you are part of a Union or participated in a Uber-strike. As a Uber driver, you have no negotiation power over them. You only power is to go see a competitor, which has the same problem and are not numerous anyway.
Then, there is also the fact that as a "personal" contractor, if you get sick, you are fucked. You car has a problem ? Deal with it with your own money. You have no minimum salary, no paid vacation, no sick day, no protection of any kind. Whatever happen to you, Uber don't care, you are just one of their many contractor.
The status of employee brings a lot of protection that worker all over the world had to fight for. This type of unipersonnal contractor just bring us back to early 1900 worker status, and we should never accept that.
Haven't heard about it in a while, but this is a goal of the current CEO: http://fortune.com/2018/10/04/uber-driver-benefits-insurance...
I think what the OP was getting at is perhaps US centric, but basically Uber would be a lot better gig if you could be an Uber driver and have good health coverage (because it was a social service). At that point the argument would only be about fair wages, which is an easier case to make.