Thank you for writing this. The bias piece is particularly important: black drivers are tipped 1/3 less than white drivers (by both black and white passengers). By my estimates, this could result in black full-time Lyft drivers (where 70% tip) earning $2,500/year less than their white counterparts.
The argument that this is still incremental earnings ignores Uber’s adaptive pricing model and other principles of supply and demand. If tipping became customary, it would cannibalize organic fares via less surge pricing, more circling, etc.