Barbara Ehrenreich makes a good point in Bright-Sided: How Positive Thinking is Undermining America. The dark side of positive thinking is the belief that if bad things happen to you it is your fault because you had a bad attitude. She details the ways in which the purveyors of positive thinking urge their followers to banish all negative thoughts because they drew bad actions. It is a short step to conclude that if bad actions occur to someone, they must have attracted them by their bad thinking.
Ehrenreich suggests, though does not actually document, that some corporations that are very enamored of positive thinking actually fire people for having negative thoughts.
Positive thinking today focuses mostly on getting money. This is true even in "health and wealth gospel" churches, where the emphasis these days is more on the wealth than the health. This is different from the nineteenth century, when mind cure and New Thought focused more on health. The dark side of today's positive thinking, therefore, leads to the idea that if people are poor, it is their own fault. Positive thinking rejects structural explanations for poverty - global recessions, corporate outsourcing, massive layoffs, etc. - and emphasizes only individual attitudes.
This explains to me why many otherwise Christian people that I meet object to programs that help poor people. They don't usually offer economic arguments about "bad incentives" and "moral hazard." They don't offer old-fashioned Protestant work ethic arguments about "laziness" or "fecklessness" (I told you it was old-fashioned). Instead, they think that poor people have chosen to have a negative attitude, which is why they are poor. If they stay poor long enough, I think this argument goes, they will see that they need to change their attitude, to just think positively.