The medical value of vaccination is hard to argue against. We're talking millions of deaths prevented per year because we've controlled or eliminated nearly a dozen deadly and debilitating diseases.
Still, the trade off is that it can result in several deaths per year due to the vaccine itself, and the vaccines, as safe as they are, have acceptable side effects and problems that affect a small portion of the population.
The only thing, though, that people can really say against vaccines in general right now, since there's little scientific evidence to support them otherwise, is that they don't believe the government should be able to medicate them against their will. If the government had that power, they might as well get back into sterilizing people with bad genes, and get rid of all the genetic diseases as well.