[throwaway22032]

I don't really agree with your premise because you are not incorporating the positive contributions of additional users.

Take the metro as an example. Each additional user is another person in my personal space, they could be smelly, they might mean that I have to stand or scrunch me up in a narrow seat. They make it slower for me to exit the station when there are queues. They could give me airborne diseases like COVID or whatever.

Those are the negatives.

But without that scale the metro isn't viable, you can't have a train system that only one person uses, so the additional people are useful. They fund it, they campaign to have it put in, etc etc.

The same is true of the road network. Yes, cars being parked on my road affect my quality of life, but the fact that other people drive increases my quality of life because we collectively pay for the road network, petrol stations, R&D into new car designs, we agree that street parking is collectively useful even if that blue car across the road is in the way for me personally, etc.

There is a critical point for both systems at which there are just too many people. I would argue that most humans don't actually enjoy huge population density and are just forced into it by economic factors (e.g. all of the best jobs in the UK are in London).