Do I need to focus on one specific career path in my admissions essay?

Hi Stratus Prep, thanks very much for the help you've provided so far.
While I'm still 3 years out from applying to an MBA, I'm thinking about how to answer the "Why do you want an MBA?" essay question in my application. Specifically, I'm wondering if I need to lay out one specific career path that I plan to pursue, or if I can mention two options that I'm interested in.

I plan to specialize in nonprofit administration after I complete my MBA, but I imagine that's too general a goal to discuss in an essay. My main post-MBA (and post-Master of Social Work) interest is social services administration. I hope to manage a nonprofit that helps people become self-sufficient by providing case management, and by connecting them to employment, healthcare, and education resources. However, I could also see myself working in mental health administration at a nonprofit or private agency.

I'm passionate about both of these fields, and to be honest there's a ton of overlap between them (which I'm learning in my Master of Social Work program). However, would it be bad to mention both of them in my "Why I want an MBA" essay? Should I write about just social services administration or mental health administration? I don't want the admissions folks to think that I'm unsure about how I want to utilize my MBA. At the same time, I really could see myself using the MBA in both areas after I graduate.

I could also try writing that I plan to focus on nonprofit administration, and social services administration in particular. This would imply that social services administration isn't the only nonprofit work that I could see myself doing.

By the time I apply, I expect to have some valuable post-MSW work experience in one or both of these areas, but if all my experience is in the mental health field, or in the social services field, perhaps that will guide the path I should take in my essay. And of course, I may end up feeling especially drawn to one field or the other by the time I apply, so that can guide my essay too.

Thanks for your help! If it makes a difference, the schools I'm planning to apply to are Yale, Columbia, Georgetown, Harvard, Cornell, Wharton, Boston College, and Notre Dame. Not surprisingly, I plan to concentrate on nonprofit management as an MBA student.