The confusion you are spreading is the same as ignoring the difference between HIV and AIDs. If a vaccine was developed that prevented an HIV infection from causing AIDs, you would be the guy telling people it's safe to have unprotected sex even if you have HIV, as long as you're vaccinated. The mRNA vaccine does not prevent the infection from taking place, it prevents the infection from developing into the disease.

mRNA vaccines do not prevent the spread of SARS-COV-2, they are highly effective at preventing a SARS-COV-2 infection from causing COVID-19.