People move around. Americans are a very mobile people. We travel to many places in our lifetimes. Also, tourists and workers from all over the world come to our communities. Thus, children should be vaccinated for serious and/or very contagious diseases, even if such diseases are not here at the moment.
SAFETY !! A famous movie line is " do you feel lucky today?" these diseases are rare because we do immunize.They are not extinct. Because of increased mobility in the world there are outbreaks with complications including death occurring. The outbreaks tend to occur in areas where children are less immunized. By not safely immunizing, we gamble with the chidren's health. Do you feel lucky?
They are uncommon... ...Most probably because most of your neighbors are smart enough to vaccinate their children against them. If you choose to forgo these immunizations, better hope your neighbors continue to protect you by making better choices. Of course, this won't help you if you go somewhere else.
Why vaccinate??? We now live in a global world. While you may not be in an area that has polio, a person from that area may visit our country, your church, your community. Then, if your child is not vaccinated, the are susceptible to the disease. Also, your child may someday be an international ambasador to some great foreign country where these diseases still exist, and you want them to be immune!
Better safe than sry. Many diseases aren't common because we vaccinate-- once populations decrease vaccination rates, diseases come back (see pertussis now in california, or measles in the uk.) also, just because a disease is not common doesn't mean it's not there at all. The vaccines are much, much safer than getting the disease.
Your civic duty. The idea of being a responsible member of a community may not be popular nowadays, but having your children immunized maintains herd immunity and prevents epidemics from beginning. With the return of diseases thanks to anti-vaxxers, there is a huge public backlash against this. Be responsible. I know you don't your kid to make an entire school sick -- and this is what happens.
International travel. As long as a disease exists somewhere in the world your kid is at risk.These diseases can spread while someone is incubating them (no symptoms).Infected people can get on a plane & travel to your city & be in your grocery store/mall the next day.By the time you realize your kid has been exposed, it may be too late and they will suffer the consequences.Believe what you wish,the risk remains.