Even worse. Drivers rate passengers. If you don't tip well they could rate you lower which would discourage other drivers from accepting your ride request.

I don't see tipping as universally a terrible practice. Sure, if a driver goes above and beyond in some way, I'll put in a bit extra. But as a routine?

It's not hard for me to see this developing into conversations along the following:

"Um, tips aren't included you know."

"I don't have any change."

"Here let me make you some."

"I really don't."

'Tips are really expected."

"Fine, here's $2."

"That all?"

"Yes"

You: Rate 2 out of 5.

Riders receive ratings, too.

Then it's all out war in the making. Suppose one takes a ride and the driver strikes a conversation about tips and how they're essential and so on. And the passenger doesn't tip. Then the passenger can assume the driver will give him low rating. So in return the passenger will give the driver really low rating.