One of the issues that isn't addressed in these debates is the poor data about truly unvaccinated children. One thing to be aware of is that some of the "personal belief exemption" data may have some flaws related to poorly-interpreted data. In some cases, it may overstate the presence of anti-vaccination communities. That is, some of those listed as PBE are still vaccinated but nevertheless chose the "PBE exemption."
I know of at least a dozen fully-vaccinated children in public school in an affluent school district in California, whose parents are scientists, engineers, and medical researchers, who have moved to California for work. Enrolling a child in a California public school is a often morass of paperwork. In particular, there needs to be documentation of vaccination or you need to select the "PBE" exemption. (Or other exemptions, including the genuine medical exemptions for compromised immune system, etc.) The requirements of documentation are onerous, particularly for people who are busy getting settled with new housing, new jobs, and many other issues. Vaccination records from an out-of-state doctor are generally not considered sufficient. It is possible, upon moving to CA, to get new primary care physicians for your children, make appointments, and get the proper certification. However, that takes a good deal of time (months in many communities) and is considered by many people a waste of resources. A number of school administrators recommend to arriving parents that rather than deal with the documentation (and keep their children at home until the paperwork is all sorted out), they merely check the "PBE" box on the form, which takes one second and no money. The "personal belief" was simply that the documentation was overly onerous for people who had better things to do than waste time satisfying unusually specific documentation requirements.
The media reports of "anti-vaccination communities are common in affluent school districts" may instead be merely that a number of affluent school districts have clued in the new arrivals that they can avoid trouble by claiming the PBE. A school district where the enrollment staff informs people about the PBE option as a way to avoid paperwork appears, when looking at the data, to be a school district filled with anti-vaccination morons.
There is much more reliable data about incoming kindergartners- these children, sometimes new to school of any type, are generally already California residents with California doctors, and the chance that a PBE exemption for them does indicate that their parents are nutballs is much higher. But the overall data needs to be viewed with a more critical eye.