I agree with your second point (self-driving cars might make more efficient use of roads), but I don't see how cheaper taxis is going to reduce road congestion?
It gets rid of parked cars, people looking for parking, etc. Also, you can service a dense city with a relatively small amount of taxis ensure they are not ridiculous SUVs, etc. And of course they can coordinate their actions and make better use of the roads as well. Then finally, if people would share rides, it gets even better.
But if taking a car gets cheaper, people who now walk, cycle, or take a bus will start taking cars.
Also, with self-driving cars that are cheaper, I expect that people who now drive a car to the suburbs will move further out of town to get cheaper housing because a) driving is cheaper and b) self-driving would mean they can do things on their commute (work, watch Netflix, etc)
I think the uncomfortable truth is that, to fight climate change, we must give up some luxuries. Flying, driving a car, electricity, low priced almost disposable clothing, electronics gadgets, etc. must get more expensive.
True, but there's a difference between owning a car and taking a car. Flying and driving will be a lot more sustainable once that goes electric. If lots of people take autonomous vehicles to get from A to B and we can find ways where that is sustainable; I have nothing against building more infrastructure to support that.
In any case this article was about road congestion; not about saving the planet. When it comes to that, I don't really believe in technical martyrdom where people voluntarily choose to not do lots of things they would like to do as a solution. And making you feel good about you through voluntarily declining to do certain things is nice and nobel but more of a form of hedonism than a practical solution. Nothing wrong with that but it's not a scalable solution in the sense that in the bigger picture of 7-9 billion people not following your lead, it's going to be statistically meaningless/irrelevant unless you convince them otherwise at unprecedented scale.