Fact is that every time you create a new way to earn money some people will do it full time no matter the feasibility. So basically you argue that we should have the current wage-slave economy forever instead of giving workers more choice. The only reason Uber is even a hint of a problem today is that we only have a single occupation following this model, but if it was more widespread and you could pick between a plethora of different things to earn money by as easily as Uber then suddenly the problems with Uber today would disappear instantly.

I understand that the current wage-slave model is better for employers, workers can't go home early if they feel tired that day for less pay since it would get them fired. Instead they have to tough out their hours every day. Similarly if a part time worker wanted a bit of extra money they could just choose to work more a few times, but that is also impossible in the current model. It assumes that workers are like machines who reliably work XX hours per week with no deviations. And even hourly jobs requires you to pick shifts beforehand and often you can't even get as many hours as you want or need, and you can still get fired for picking too few shifts etc.

So I feel that Uber is a much more humane way to handle labor than current employment contracts.