Some people can't get vaccinated because of medical reasons. Also vaccinations do not have a 100% effectiveness.
And sometimes the best of hammers will mangle a perfectly good nail. Yes, the tools we have are imperfect; no one is disputing that.
If too many people decide to not get vaccinated
Whoa whoa whoa, stop right there. The default state of a human body is unvaccinated. No one is removing a vaccine from themselves. No one is removing antibodies from themselves in an effort to make themselves or others more susceptible to disease. The default state is unvaccinated. It isn't about "if too many people decide not to", it's "if enough people decide to do it... positive things can happen". And yes, there's a huge difference. See the previous post.
then an outbreak could spread through all of those people and the ones where the vaccination didn't take as well as the people who could not get a vaccination. If the percentage of people who were successfully vaccinated is high enough then you will have individual cases here and there.
I completely understand that. However, you need to understand that disease is part of the human existence. Don't want to deal with disease? Stop being alive; that fixes the problem. Otherwise, accept the existence of risk and understand that your desire to minimize your risk and the risk of your loved ones does not entitle you or the government to strap a child to a gurney, jam needles in their arm, and pump them full of drugs (albeit very good and beneficial drugs).
Vaccines are a wonderful tool of modern medicine. The fact that that tool's effectiveness increases when more people make use of it does not entitle you or anyone else to force others to make use of that tool. You are not entitled to a risk-free or even a risk-reduced existence. The default state of a human being is naked, defenseless, and susceptible to all manner of diseases and predators. The fact that you're now safer than any other human being in the history of the planet ought to be enough. You have no right to perfect safety and you have no right to force others to help you get closer to perfect safety.