The ironic thing is, generally speaking, antivaxxers tend to be on the left of the political spectrum. I sincerely doubt Bachmann is trying to get their vote. More likely, she is just displaying more of her antiscience predilections like creationism and global warming denialism. This just goes to show that when you go far enough to the left or right, both sides wind up meeting on the far-side of the moon.
I think conspiracy theories surrounding vaccination and other medical services are insidious because they have a profound, direct effect on the human health. Medical science provides a truly stunning array of vaccines and treatments that are being unfairly and ignorantly assaulted by conspiracy theorists, the result of which is that fewer people are willing to care for their health that way.