A few possibilities: 1. Vaccines aren't 100% effective. Unvaccinated people are a threat to vaccinated people. 2. Vaccines aren't an option for 100% of people

A few possibilities: 1. Vaccines aren't 100% effective. Unvaccinated people are a threat to vaccinated people. 2. Vaccines aren't an option for 100% of people. People who choose not to vaccinated people are a threat to people who can't be safely vaccinated. 3. Information, including misinformation, spreads more quickly than death does. It won't die out due to natural selection. 4. Losing half our population to infectious disease, even if you consider them stupid and irresponsible, would have catastrophic effects for the economy. 5. A majority of the effected population are children. 6. Maybe, just maybe, letting millions of people just die of preventable disease, even if they're adults and made a foolish decision, isn't the right thing to do.