That's a terrible argument, if anything you can argue that seatbelts don't prevent death upon accident, but they do reduce the chance of death.

Seatbelts were never advertised as preventing accidents (infection), but vaccines were infact advertised as 95% effective in USA and 100% effective against infection in Africa. Most importantly, claims were made by medical professionals that even if you happened to be infected by the virus, you would be a dead end to it, ie you won't transmit it to others. Transmission was the main selling point of the mandates.

“When you get vaccinated, you not only protect your own health and that of the family but also you contribute to the community health by preventing the spread of the virus throughout the community,” Fauci said. “In other words, you become a dead end to the virus. And when there are a lot of dead ends around, the virus is not going to go anywhere. And that’s when you get a point that you have a markedly diminished rate of infection in the community.”