It is not designed to help the people who actually own the computers that are being forced to re-choose their software.
It actually does help them, because their own stupidity will be limited by the capabilities of the browser they choose. So if you gave them IE by default, the most clueless users would catch every IE/Windows related malware. But if they have Mozilla or Opera, then they'll be immune to IE malware, and since Mozilla and Opera have a smaller marketshare, they'll be exposed to statistically fewer attacks.
Sometimes, users must be saved from themselves, and this ballot screen is a good start.