system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If immunizations are supposed to prevent you from contracting certain diseases, then why is it such a big deal when some people choose not to get them?
gpt
threefold:

1. Because the more people unvaccinated, the more opportunity there is for the virus to reproduce, and the more likely it will be able to mutate enough to infect people who were vaccinated.
2. Not everyone can get a vaccine due to medical issues, those who can't get it are at more risk the more people who are around who choose not to get it.  In effect there is already an unvaccinated group by default, making it bigger (for no reason) makes #1 more of an issue.
3. People choose for others (their children) if they get vaccinated or not, so there is some concern for those who didn't willfully choose to avoid a vaccination.