of course it is dangerous. but if you are employed by uber and get hurt "on the job" while carrying out their agenda, they should be responsible for your recovery.
You can look at it as a service connecting bike messengers to people that need deliveries.
A comparable example is Google Play or the Apple store. They take a cut of your pay by connecting you to customers but they don't call you an employee. Where is the uproar there?
When I sell something on eBay I don't have any expectations that I'm an eBay employee. The Google Play and Apple app store are both apt analogies as well. Selling goods or services on a marketplace often comes at a cost per transaction, but it almost never comes with an expectation of employment.