I totally agree with you. I L. when people say "I was raised on X and I'm perfectly healthy!" and it's like...no you're not. I have a friend who says this all the time and I try not to laugh because she is so not anywhere near the picture of health. Neither am I, but I don't claim what she does.
Anyway...my response to anyone who actually engages me over my decisions is "I believe that you do what you know and when you know better, you do better" and leave it at that. And then I focus on the like-minded parents I know.
A woman in my town just wrote a book called Little Changes, which is about all the choices we can make every day that will be healthier for ourselves, our kids, and the environment. I am lucky to be plugged into a widening circle of local parents who feel the way I do about things. Who don't think it's wacky to question vaccines, or try natural remedies and whole food supplements to try to help our bodies and minds heal themselves. Who garden at home or belong to the CSA and frequent the farmers' markets. Who use non-toxic cleaning products and carry tote bags into the grocery store. Who breastfed if possible and made baby food at home or cloth diapered. Who are concerned about lead, mercury, fluoride, preservatives, artificial colors, toxins in our skin care products, plastics, and GMO foods. Who use booster seats until their kids are 80 lbs and go rear-facing until they're 2 or 3. Who look around at all of the ADHD, Autism, Allergies and Asthma and think "my God our kids are the canaries in the coal mine and something is majorly, systemically wrong with our environment and health care."
Just know that in time, if you're not sanctimonious or pushy, if you just live your life with a thirst for knowledge and quiet conviction, people who doubt you may later find their way to you. When conventional medicine doesn't seem to have the answer, when something in the news catches their attention, etc. your friends and family might turn think "you know who might have heard about this...?" and think of you. And then you have the opportunity to gently share what you know. Recommend a book or a website. Point them in the right direction and when ready, they may join you on whatever part of your journey is valuable to them.
One of the funniest examples of this is my parents. My mother is an RN and trained and worked in traditional medicine but she has been into "alternative" medicine for 30 years. She's about 10 years ahead of the mainstream when it comes to natural medicine. My father thought she was full of it and would never listen to her or take her advice. Then 5 or 10 years after she recommended something (like vitamin E and fish oil and niacin for cholesterol control and heart health), one of his doctors would recommend it and he'd embrace it like it's cutting edge news. Somehow he became a fan of Dr. Mercola, who is pretty edgy, and my dad thinks he is the be all end all and my mom is just sitting back biting her tongue trying to not say "I told you so." It's really funny to talk to my dad now and have him go on and on about the inflammatory effects of many grains, insulin resistance and the roles they play in heart health.
So again, just stick to something simple (you do what you know and when you know better, you do better works really well for me) and change the subject.