Why do I have to vaccinate my child?

To save their life. Prior to vaccinations, thousands of children died each year from infections. Vaccines were developed to enable children (and adults) to develop protection against these illnesses. Except for smallpox, all of the vaccine-preventable diseases are still present somewhere. All it takes is for an unimmunized child to come in contact with someone with the disease to contract that illness.
Why Gamble? Immunizations may be the single safest, most effective heath intervention produced in the last 100 years. They are proven to be 99% effective, safe and have saved literally millions of children's lives. A caring, educated parent immunizes.
Many reasons . . . Because getting immunity from a tiny shot is better than suffering paralyzing polio. Because we're all in this world together, it is unethical for some people to benefit from others' getting vaccinated, while they themselves don't get vaccinated. It's a small planet, so everybody takes the minuscule risks from vaccines, and everybody enjoys herd immunity and the benefits of a healthy population.
Please vaccinate. Vaccines are extremely important for children. Recently, diseases like pertussis, mumps, measles, and diphtheria have been on the rise in our country because children are not being vaccinated. Pertussis and diphtheria are extremely deadly and mumps can cause infertility it males later in life. In order to keep these diseases at bay vaccinations need to be given.
Its the law. We are both blessed and cursed by how well vaccination programs have worked. We no longer see most of the diseases we vaccinate for. Most doctors now couldn't diagnose some of those diseases because we have never seen them. The reason you have to vaccinate is that one of the strong points of vaccination is herd immunity. The more people immunized, the less likely of a bug making the rounds.
Avoid faulty idea. Many assume that since everyone else got theirs you don't need to worry about your kids.Wrong! We lost 40 infants last year to whooping cough with that reasoning when we lost none/yr in the 90's.As long as we have international air travel, someone incubating a disease can arrive from anywhere in the world and bring it to your mall or supermarket the next day.