Why are some parents against vaccinating their kids?

There is a lot of controversy about vacinations, both with humans as well as animals, for instance, I was never vacinated as a child because of my mothers religious beliefs, so when my oldest got her first polio, I wasn't allowed to change her diaper for 2 weeks because she was shluffing live virus. I have since been vacinated, but I never did agree with live oral polio vaccine, so my oldest had it once and after that all my kids had the killed injection, and go figure, now that is all they give. Some parents believe that the benifits do not out way the risk. My kids were never given whooping cough vaccine because the research I was directly involved with proved the risk of the vaccine far out weighed the benefit. There is also controversy as to how often vaccine needs to be given. We know for instance in dogs and cat that yearly vaccination unnecessary, every 3 to 5 years after their initial vaccination group is sufficent, but municipalitys still require it yearly, we have seen a great increase in cancer in animals vacinated yearly. Some vaccines are also associated with higher incedence of allergies, autisim (the new en vogue disease) and certain types of cancer. I don't see how anyone can associate it with cerabal palsey when that is proven to be a birth injury, but some researchers do. I actually have a 13 page article on it that I published in JAMA several years ago, if you are interested, I will e-mail it to you.