I don’t know if it’s that straightforward of a comparison—while it may be true that taxis are bad for traffic, you have to take into account what the use of them is: transporting people around. If you consider the alternative where taxis don’t exist, at least some percentage of taxi passengers would probably just bring their own personal cars into the city, thus making traffic much worse.

Thus, though it’s true that the impact of taxis on traffic is significant, the alternative is much worse. People still need to get around.