What are some candidates for worst technology still in use today?
Nuclear Weapons / Power
Automobiles kill 40,000 people a year, as many as soldiers that were killed in the Vietnam War.
The infrastructure to support automobiles destroys landscapes, creates unsustainable suburban land use, and depletes non-renewable fossil fuels.
The evils of television have been well documented in books such as Gerry Mander's In the Absence of the Sacred. My biggest gripe is that it programs people to be little consumer robots.
The average adult sees 20,000 commercials every year. That's 20,000 times a person hears a message "You aren't good enough unless you buy something."
Nuclear weapons, obviously because of their huge destructive power. But also nuclear power because we don't know what to do with the waste.