Applying to American Studies/Literature PhD Programs without ultra specific area of focus or career goals - Bad Idea?

[bgt28]

I'm curious: what do people make of the fact that so many people say it is a HORRIBLE idea to pursue a PhD if you don't have an ultra-specific topic of interest in mind, or equally specific career goals for the degree? What's the issue with using the degree to explore established interests? Or is the reticence more related to having a weaker statement of purpose?