I don't understand why people who vaccinate are afraid of those that don't.
It's not fear, but there are several legitimate reasons to be concerned about people who choose not to vaccinate their children for personal non-medical reasons:
1) Some people have legitimate medical reasons why they cannot receive vaccines or it is harder for them to get vaccines, e.g. allergies.
2) Vaccines are not 100% effective but increasing vaccination rate provides greater protection to all.
3) We still care about kids who are not our own and we don't want them to catch easily preventable diseases like measles.