There is a serious answer to this that will immediately be dismissed so I don't know why I'm bothering but here we go.
First, there is the mutation issue. The more bodies the virus infects, the higher the likelihood of mutation. Mother nature is not very strategic and most of these mutations will either have no effect or will make the virus weaker. The bad news is that viruses are basically just stray DNA and mutate pretty quickly because they are only a few strands of protein, and the mechanics of replication are not exact in the slightest. Each time this happens there is a chance the virus may become more deadly or infect people who are previously vaccinated. Vaccines aren't magic potions, they create physical barriers at the cellular level that help protect (but not PREVENT) infection.
Second, immune response is not uniform. A vaccinated person is not magically immune to a virus. Instead, their body produces a biological agent that can help prevent a virus from grafting to a cell. Some people will produce more of these agents than others. People can still get sick if they are vaccinated, they're just less likely to die. It can still put you out of work for a week.
Finally things are not as simple as 'vaccinated' or 'unvaccinated'. Children for example aren't generally vaccinated so Cletus, or more likely Cletus's children, can infect my children. There are people whose immune systems will not allow them to get vaccines for whatever reason, and Cletus puts them in danger. Yes, this means this class of people who cannot get vaccines are exactly the same risk as Cletus except they are more likely to die (probably).
I support people's right to choose not to get vaccinated, so long as they are aware of what harm they are doing to the population.
