Things are relatively simple.
Vaccines work for whole populations, not necessarily for individuals. In order to make them acceptable those who market them try (or at least should try) to make them as good as possible.
For a rational (but callous) individual the best thing to do is to make sure that he is the only one not vaccinated: he cannot catch the disease since nobody can have it yet suffers no possible side effects from being inoculated.
If enough people opt out then the whole effort would have been in vain. The immunity obtained by vaccination isn’t as strong as the one one gets after surviving the disease so if enough people get the disease because they haven’t been vaccinated at all then older people, those who have been vaccinated first, start to fall ill.
From this point on nobody would vaccinate anymore their children – because it’s useless, right? – while the right thing to do would be to get a second vaccine, a rappel.
What’s getting on my nerves is the fact that sometimes we trust ‘scientists’/’technicians’ with our lives (for instance when we get aboard airplanes) yet other times we develop all kind of wild theories (about vaccines, for instance).
Of course we need to be extremely careful, both when choosing an airline or a pharmaceutical company, but to refuse altogether to fly or to vaccinate your children…