I have to say that the whole notion of an SPA is weird. If we had a noted expert on lichens editing, we wouldn't object to him editing solely in that field. And if we had someone who had extensively studied lesbianism in Edwardian England (a far more controversial subject) it would be reasonable for her to concentrate her efforts on such articles. There are obviously people who are on Wikipedia on A Mission, but some of those missions are appropriate, even when some people feel that they are POV (which can just mean that the current article is badly biased). It's dangerous to one's neutrality to do that, of course, but it isn't necessarily wrong.