Cars kill more than 1 million people a year, and are actively cooking our planet. On balance, cars -- at least our ability to use them -- has been a huge negative.
The Internet is a lot more balanced, but both show how a lack of foresight and system design can lead to a lot of negative consequences. We could drastically cut down on the number of road deaths if we took it more seriously and made some big system design changes, but we haven't. We can also make the Internet a better place, but there will always be issue with all massive systems.