In the US, in Manhattan, you can probably make do. And there are other cities where you can probably manage with some combination of Uber and short-/longer-term rentals. And just foreclose on certain types of activities for the most part. But I suspect for a lot of people out of school, "I don't need a car" means the same thing I did as an undergrad, namely lean on people who had one.
You can get by in a lot of cities, like Seattle, without a car if you don’t have kids. You don’t even need to bum rides. Even in LA, I wouldn’t have bought a car if it wasn’t for my wife getting pregnant.
In Boston/Cambridge I could probably get by if I mostly didn't leave the city but I know lots of people outside the city and I do lots of activities that would be outside the city. Unlike Manhattan, the assumption is that you have a car as an adult if you aren't right out of school. There's one job I had (for about 1.5 years) that I could have managed without a car.
I think you're generally OK if most of your activities work via transit and Uber. As you suggest, as well, kids and pets probably make things more difficult.
In several parts of Seattle you genuinely don't need a car, with few compromises. Virtually everything is walkable. Even many of the popular trailheads in the mountains have seasonal bus service. Just about the only time I use public transportation is when I take light rail to the airport. I know quite a few people that live this way.
I do own a car but that is only ever used for traveling to another State or to get into more remote parts of the mountains. For anything else, using a car would be inconvenient.
I'd probably be similar if I lived in Boston/Cambridge these days without a need to commute. I wouldn't use a car day to day. But I'd use one to go to outdoor activities or to visit people outside the city. Even if the economics didn't quite work out, I'd want one customized for my liking just so I didn't need to think about it.
