Why should advertisers not advertise on Glen Beck's show? For those who don't know, Beck opined on his show that President Obama has "a deep-seated hatred for white people or the white culture. . . I'm not saying he doesn't like white people. I'm saying he has a problem. This guy is, I believe, a racist." That's an opinion as well.
Beck's opinion is, to most, more inflammatory than Mackey's, but that can make Mackey's all the more dangerous (if you're someone who would like to see public healthcare). The fact is that Mackey seems to be a liberal of sorts (in fact, Whole Foods offers health insurance to their employees) and an at least somewhat successful business person (I don't actually know enough about Whole Foods, but they don't seem to be going bankrupt).
So, his words are quite a threat to the agenda of those who would like to see a public health plan. And his words have that much more power because they're coming from someone who seems to have liberal leanings and is running a business that does provide health care to their employees. If someone is advocating for the opposite of what you would like, should you not take that into consideration? We vote with our feet every day. He took action against public health care in trying to change people's opinions through his piece. I know many who stopped buying CDs because of the RIAA's positions.
I will grant that his piece was a lot more thoughtful and measured than many have passed on, but this is an issue that is very contentious and many people feel (I'm not making any judgement here) that his words contribute to a negative impact on the possibility of a public health plan and that the lack of such a plan will have a negative impact on their life. As such, they don't want to spend their money at his business.