Yes, they have too many cars, and also make stuff not enough durable. If you (and I) do not have any children then human population of future can be reduced hopefully; currently human population is too much but that is one way to reduce in future. There is some other way as well, I think (but, you should not just kill everyone (regardless of their species) just to reduce the population; only for self-defense or for food).

We could consume half, we could even impose laws controlling consumption of resources, natality, etc, but since these would be pretty unpopular no politician would consider that unless it's probably too late.

you cannot consume half. (not talking about phones) but if a human needs X food then he cant half it. you can replace with X with half Y and half Z but the logistics is the same.

The issue is overpopulation. You need a specific amount of resources to sustain that number. you cant half it without halfing the population

How do you explain that people in US produces 4 times the average CO2 emissions?

Surely you know what that first sentence sounds like :)