I actually have a couple of reasons / points.

1. Education - outside of BB in the big wide open world i did not even know about delayed vax or non vaxing familes - i was vaccinated, we had needles through school, the Dr's mention vaccinations during pregnancy and there was never any information provided about the benefits or risks associated with vaccinating my children.
To me i just thought it's another part of parenting, you have a baby, you see the MCHN and you take your kids to get needles.

2. Emotional Points - my mum has a friend who has deformaties from polio when she was younger, she is an amazing lady and has lived a full life despite the issue she has but it pains me to watch her family suffer as those issue now impact on her as she gets older, as her poor body is so compact that things are no longer working as they should.
I made the decision out of an emotional view that i would neither want to watch my children suffer nor have them suffer through something that is and can be preventable.

3. Whooping Cough - not long after DD1 was born i get a letter from the hospital stating a staff member who ahd been working on the labor ward has tested positive to whooping cough, that we should keep a very close eye on our daughter and be wary of anything suspicious, i had watched my mum suffer through losing my brother to SIDS, there was no way i was loosing my daughter or possibly being the link to someone else loosing their child by not vaccinating my daughter.

I agree there are pro's & con's for both side of the debate, for me with DD2 i made an informed decision to continue to vaccinate her, even after reading through BB i made up my own mind that vaccinating worked for us, there was no history of reaction on either side of my family or DP's.
I wanted what was best for my girls and for me that was not to possibly have to suffer through a preventable disease OR be the person who passed on a preventable disease and possibly harming another.

I however would NEVER be upset if someone did not vaccinate their child and say whooping cough was passed on, it is THEIR decision and they would make it for reasons that suit them.