Studying People Like Yourself
1. The motivational sense: "It directly affects me, or people I identify with" is a pretty obvious and understandable motivation for choosing a subject area. It's so obvious that people often become befuddled when they can't explain someone's choice of study in these terms (especially if there's an obvious personally-relevant topic of study for that person).
2. The epistemological sense: This is the classic insider/outsider problem -- can an outsider ever really understand the thing they're studying? On this question I think pretty much everyone agrees that both insiders and outsiders have useful perspectives.
3. The political sense: In studying a group, you're setting yourself up to in some way speak for them, producing authoritative representations of their situation. But speaking for some group becomes ethically/politically sticky when there is a power differential between your group and the group you're studying. One of the key techniques of oppression is that the oppressor claims the right and the ability to speak for the oppressed -- white people have long been the ones making the official pronouncements on what black people are all about, men get to define womanhood, abled doctors are the source of information about the disabled, etc. The voices of the oppressed are crowded out, either by being overtly excluded (eg denying members of some group a place in academia) or by being drowned out because the oppressor group's voice is amplified by their financial, status, and other types of resources. The ability to speak for and define oneself is a key right claimed by liberation movements. Thus, to study a group that is oppressed relative to you is in some way to perpetuate the oppressor's claim to speak for the oppressed. This is not to say that members of oppressor group can never study the oppressed -- after all, oppression is multidimensional and your study may still be a net oppression-reducer. But concern about the politics of speaking for others is still a real concern.
My dissertation research raises questions about studying others in the first two senses, since I'm a Pennsylvanian with no experience of wildfire* studying what people in New Jersey and New South Wales think about wildfires. But it doesn't raise questions in the third sense, because Pennsylvania vs New Jersey, the US vs Australia, and people with vs without wildfire experience are not significant axes of oppression or power differential. And on many of potential power axes, I'm actually an insider with respect to my study population -- we're both largely white, middle-class, and from a semi-rural background.
For my other research project, on community involvement in Superfund cleanups**, however, there is a political question. For our Waukegan case study, one important part of our study involves looking at the views of the Latino community. So I am to some degree a white person speaking for a group of Latinos. However, that alone doesn't revoke my right to do this study, because I would argue that the net effect of the study is to reduce oppression. At the moment, the Latinos in Waukegan have very little voice of any sort, and are often spoken for by whites who (while in my experience invariably well-meaning) lack broad, systematic knowledge of what Latinos think about the harbor cleanup. Our research, being based on listening to the Latino community, is able to both speak more authentically for them as well as pave the way for their voices to be heard more loudly and directly in the cleanup process itself (in Waukegan and hopefully elsewhere). Or at least that's the theory by which I would claim a right to do research on people of another race in this situation.
As for whether this concern is increasing, I would suspect that it is for all three senses. The growing diversity of the academy means that many areas of study now have more people who can study them due to personal connection (including areas of study that didn't even exist until the academy had a critical mass of directly involved people). With respect to the epistemological sense, I think we're increasingly recognizing how deeply culture shapes our understanding of the world, with the result that the special insights of insiders are gaining prominence relative to the insights of outsiders. And in the political sense, the moral/political shift associated with the rise of "identity politics" has brought questions of speaking for others to the forefront.
*Judging from the conferences I've been to, I think I'm the only person studying wildfires in the US who isn't a former firefighter.
**Which I'm in one sense more of an insider to, having grown up in a Superfund site. I even wrote a paper (.doc) on my hometown for an Environmental Justice class long ago, which I may one day revise into something publishable.