I think it is fairly easy to understand why it is desirable to have as much of the population vaccinated as possible. First, like anything biological, the risk

I think it is fairly easy to understand why it is desirable to have as much of the population vaccinated as possible. First, like anything biological, the risk of COVID is not a binary quantity. There is a very strong correlation between the severity of the disease and certain factors such as age. Still, even relatively young people can and do get very sick occasionally. This is why public health agencies make risk/benefit analyses for the vaccinations in different age groups. In many countries they have concluded that the benefits of mRNA vaccines vastly exceed the risk due to observed side effects in all adult age groups. This means that getting as many people vaccinated as possible reduces the disease load in the population, which is a central public health goal. Second, SARS-CoV2 is a very infectious novel virus with no widespread population immunity. This means that if left unchecked, it can spread extremely rapidly. Even if the "high risk" groups are mostly vaccinated, a very large number of "low risk" people can get seriously ill at the same time. This can easily overwhelm the healthcare system even in wealthy countries. Fully vaccinating the "low risk" population significantly reduces this burden.