This is my #1 most desired feature on Uber and Lyft.
It's not irrational to want to reduce one's environmental impact without bearing that level of inconvenience, even if one could reduce it to a greater extent by spending the extra time.
There are literally millions of used cars that will ultimately be less harmful over their lifespans than increasing the demand for new vehicles. You can't only take into consideration mileage, but must also consider the environmental cost of production, logistics, and electricity generation.
If you're going to whittle that argument down further by saying you _want_ a new car anyway, or you're drawn to reduced maintenance/fuel costs... you might as well admit that you don't actually care about the environment and just want a cool car (I won't knock that, but don't pretend that virtue is your motivation).
except we're not talking about buying a new car. We're talking about using uber/lyft.
If that uber driver is does uber-driving full time, and they charge their car using a suitably green power source, then the electric car might be seeing enough use/mileage that the emissions savings make a net win after a year or so on the road.
Maybe uber-consisting-of-only-cars-at-least-10-years-old would still be better. But you're never going to get uber to implement that.
And of course taking the bus is better, but sometimes extremely inconvenient (for some definition of "extremely".
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Separate line of thought - I have in the past reasoned thus:
In the year 2025, millions of new cars will be produced and sold. There is nothing that a couple of curmudgeons like you and I can do about that. But the fraction of those cars that are electric vs petroleum-powered is going to depend on the number of people who by electric cars between now and then. Consumer behavior does influence the set of products that vendors make available to consume in subsequent months and years. So maybe these brand-new-electric-car-buyers are actually helping in an indirect (and impractical-to-quantify) way.