I think it works for some people who love to teach and can write despite the teaching. The problem can be what you have to teach. If you get saddled with a bunch of freshman comp classes, with 25+ students in a class, it is hard to be a good teacher and a good writer. If you can get into a position where you are teaching a more manageable load, it is possible.
Then the problem becomes spending the time and money to get the PhD (if you want the full time job) and then getting the job with the 200 other applicants. If you get an MFA, you have to deal with the people who say it isn't a real terminal degree (insert joke about it almost killing me), or those who expect extensive publication along with an MFA to get a tenure-track position. To which I always joke, "If I had the kind of publication credentials you are looking for, I wouldn't be applying for this job." Of course, not many college writing teachers find that amusing. ;-)
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Then the problem becomes spending the time and money to get the PhD (if you want the full time job) and then getting the job with the 200 other applicants. If you get an MFA, you have to deal with the people who say it isn't a real terminal degree (insert joke about it almost killing me), or those who expect extensive publication along with an MFA to get a tenure-track position. To which I always joke, "If I had the kind of publication credentials you are looking for, I wouldn't be applying for this job." Of course, not many college writing teachers find that amusing. ;-)