I have mostly vaccinated my children. And myself I do believe that, on the whole, most of these vaccines are effective and thus do more good than harm. I also believe that broad vaccination programs do extend protection across the population - so there's a social/community good angle for me too.
At an individual level, however, I also believe there are some very valid reasons not to vaccinate.
I have considered the risk/benefit of each and made decisions accordingly. In some instances I have gotten vaccinations that I'm not entirely happy with simply because they are bundled together with others that I do want. We have no family history of negative reactions to vaccinations or any other contraindications (that I'm aware of), but with some illnesses - like varicella for instance - I'm not sure the risk of the vaccination is really worth the possible benefit.

- Just because some of the comments here got my thinking....
The reason I vaccinate is not because I'd never forgive myself if my child was seriously ill or died from something preventable. Potentially, practically anything is preventable... if only we'd stayed home that day... if only I'd been watching more closely... if only.... I don't like it but I can't control everything. And vaccines are not 100% effective - in some cases not even close. It's about risk mitigation, certainly, but I have to balance the risk of inaction against the risk of action and it's not as clear cut as - this will stop my child getting whooping cough (or whatever). Just a thought