Bottom line to me Uber is excellent way to improve the amount of car pooling we do, which HAS to be better for the environment than every one of us driving our own car carrying a single person to get where we need to go.
It's better in a whole multitude of ways. It's better because you don't need as many cars; okay, so that's only 25-33% of a vehicle's lifetime energy use, but that remains significant. The percentage decreases as our fleet ages... but the more old cars we have on the road, the more unnecessary pollution we are producing, so that's another reason to encourage vehicle sharing. And then there's the fact that a car that's being utilized constantly isn't cooling down and having to be warmed up again, so the anti-pollution catalysts are functioning more of the time. It's a massive, massive win. "Proper" taxi companies have not sprung up to feed demand, perhaps in part because of licensing schemes which have been put in place which deter them.
Ultimately, protecting the passengers is a job best done by a combination of proper driver testing and vehicle inspection, and a goddamned working national health system. You don't need massive insurance liability coverage if you have a health system which will care for you if you get smashed. The required liability insurance is only so high as it is because health care costs are out of control, and yet the liability insurance is likely to not actually cover all your health care costs in a serious accident anyway. You can't fix this by increasing the insurance, because the costs would be too high. You can only fix it by fixing health care. But here we sit, arguing about whether people should be able to use their cars as they see fit. If they're not capable of that, they're not capable of driving, and you should just take the car away already.