I think this really depends of the network you are talking about. In some European cities, public transit networks are a blast to use. If frequencies are high enough, and modalities are well connected, you can "ride" the city as easily and naturally on a metro/tram/bus as you would have done by walking. I've took a lot (a damn lot) of bus/trams just because they were there, passing by, and allowed me to save 3 or 4 minutes (with my annual ticket, price was never my mind).
(But I'm lucky enough to live in one of the lowest CO2 emitting countries in terms of energy mix.)
I do remember an UberPool trip I took. We got another passenger along the way. The driver ended up having to go 8 blocks out of our trip's path to pick up the passenger. She went 1 block and then got out. At least when you take a bus or tram out of convenience you are not being so wasteful.
In fact, having lived both ways, I'd say you're far more incentivized to do this in a suburban setting with a car, since you're sitting in a private bubble with your own music and climate for every part of the trip except the store itself.