As a reader, I can choose whatever book strikes my fancy, and if I don't like it once I've gotten part way into it, I can simply stop reading it.
As an editor, the "put it down" option is nowhere to be found. If I take on a job, I finish it. That's what I'm hired to do. So there's the question: Do I have to love a genre to edit it?
The answer is a big fat NOPE.
I've edited a decent number of books from a decent number of authors, and it goes without saying that those authors don't all write at the same level of skill. If a book isn't ready for edits (major issues), then that's one thing, but if a book is ready and I take on the job, it's now a matter of accepting that the writing level is either good or waaay good. Genre really doesn't factor in.
[I should clarify: genre is only a factor if someone asks me to edit erotica. I'm no prude, but I don't think editing erotica is compatible with my job as assistant to the worship leader at a large church. Call me crazy if you must, but I'm pretty sure I'm right.]
Anyway, I've found that, regardless of my typical reading preferences, the genre of a book I'm editing doesn't matter in the big scheme of things. I've been pleasantly surprised at how much I've enjoyed certain books I wouldn't think to pick up for pleasure reading. Now that my kids are no longer of the age where I sit down to read to them—and we did read aloud to them well into their teen years as a nighttime thing so we could all enjoy a good book at the same time—I rarely pick up juvenile fiction, or even young adult fiction, and yet I enjoy editing those books when they come my way. Part of it is, I think, that it reminds me of how much discovery is out there for kids who read, and part of it is that I've just worked with good writers who tell an entertaining story.
The one thing I have to be cautious about (and I don't think I actually do this, but it's always good to be alert) is to not change an author's voice while editing something I'm not really enjoying. A few years ago, I agreed to read/review a novel for someone who approached me through Goodreads. I was between edits at the time and thought it would be nice to do a new author a favor. The book was science fiction, which I love, so I thought it would be enjoyable.
Silly me. The book was not enjoyable. It was a confusing read, because it was full of time travel and the dialogue was written in the present and future tense at the same time . . . and it took me a long time to get into the flow of it enough to read without constantly rereading. It also pushed an agenda, which I do NOT like in works of fiction, even when it's a viewpoint I might agree with. It was super lengthy, too, and was only the first part in a ten-part series, from what I gathered.
The bottom line: even though I was beta/review-reading this and not really editing per se, I had to be careful to not let my (lack of) enjoyment cloud my judgment of whether the book was ready to publish. The book was written skillfully, and the author did a heck of a job self-editing (which I would never recommend to anyone as a general rule). Though there were many things I would have wanted to change, it was just fine the way it was. I felt like a huge success just by being able to give a neutral opinion when I did my report. I told the author of my struggles with it, but she actually loved my review and thanked me for separating my reading tastes from the quality of the writing.
It may be difficult, but editing should not be a matter of opinion. I try to think of it like a doctor thinks of his/her patients. Wouldn't you always want to deal with the pleasant people who are fit and attractive? Or be the dentist whose patients all have great teeth?
Editing is like that in many ways. The manuscript is the sum of its parts, and it's my job to make sure all the parts are in the condition they're supposed to be in so the whole is at its best. It's not my job to judge whether the parts are attractive to me personally, because those same parts, when put together as a whole, will be attractive to someone else.
