Because it makes no sense. It's like being "anti-education" because a large number of schools that claim to be educating children are actually just conducting communist brainwashing. You're not actually anti-education, you'd be anti-communist brainwashing in that scenario. You shouldn't be anti-vaccine, you should be anti-ineffective/dangerous vaccines. And, even if you think that's every vaccine past and present, being anti-vaccine would require that you be against every vaccine including ones made in the future that may actually work and not be dangerous. And being against such a vaccine would be incredibly silly and immensely stupid.