Tipping at restaurants is bad enough: why do I have to decide how much the waiter should make? If you make me think about it, 20% gross honestly seems way too much: the back of the house contributes a much larger portion of the value of the meal, so it feels like I'm stiffing _them_! But tipping waiters is ingrained enough that I just always give that 20%.
Any other transaction where apps try to add tipping, though? That's going to be $0 every single time, guilt free. If anything, I feel like I'm doing my part to keep companies from ruining another social interaction.