1. Because vaccines don't provide 100% immunity. Nothing can. The more unvaccinated people there are, the more we're all exposed to the disease and the higher the risk of catching it despite being vaccinated. Also, there are people who for medical reasons (allergic reactions, compromised immune systems, still too young) can't be vaccinated. Every unvaccinated person poses a risk to them.
3. This is true. However the risks from those side-effects are far less common and less severe than the risks from the disease when you're not vaccinated. Arguing that having a 1-in-100,000 chance of being crippled for life is better than having a 1-in-1,000,000 chance of needing a week in the hospital is... not a winning argument, I'm afraid.
4. As long as it's just you or your children, fine. But it's not, you're exposing everybody else to the consequences of your decision. You want the right to control what goes in your children's bodies, yet in the same breath you say we should have no right to control what goes in our children's bodies when it comes to the infections originating from your unvaccinated children. That doesn't fly. Note that the CA bill doesn't prevent you from refusing vaccinations. It simply means you can't send your children to public schools and subject everybody else's children to involuntary exposure to your children's infections if you won't get them vaccinated. You're free to send them to a private school that doesn't require vaccinations if you want.
5. How about the family who sees the same thing happen to their kids because before they were old enough to be vaccinated they caught something from your unvaccinated kids? Are you going to take responsibility for your actions there? If so, how exactly do you propose to compensate that family for the loss of their children?