Isn' that how you end up with a leaky vaccine? https://en.wikipedia.org/wiki/Marek%27s_disease

While it seems rare, it also seems like a much deadlier outcome.

Not everyone can be vaccinated for a plethora of reasons. This would do nothing for that cohort.

That is not the case - it is for that specific variant of the disease but diseases spread through the entire population have a huge area to mutate in and one of those mutations could be quite deadly.

One of the reason there's a lot of gas behind rolling this vaccine out quickly is that we want to avoid allowing the virus enough time to mutate up some different strains that this vaccine isn't effective in preparing us for since that makes the vaccine far less effective overall.

The problem is that if the vaccinated population carries the virus, then the risk of being infected increases for the unvaccinated population. It doesn't matter if the vaccine reduces the severity of the virus if you haven't received the vaccine.

On the other hand, if the vaccine reduces the transmissibility of the virus, then everybody collectively benefits from each additional vaccination.

Untill you visit a place with a significant un-vaccinated population.

This has happened with other diseases.