I have to agree about the need for a pen name in certain cases. It's a fact of life that people become pigeonholed by whatever their primary career is. I write frivolous humor for a living. I also dabble in serious historical non-fiction essays and moody short stories. Like Tymolee says, two very different markets! When I've submitted my essays or stories to editors I know, I figured the fact they know me, at least by reputation, would help my chances of being considered for publication. Instead I usually get the opposite reaction: "You're a gagwriter, not a historian or a literary writer." When I point out that John Grisham can be considered a "lawyer not a writer" or that Woody Allen was also a "gag writer not a movie director", they don't get the point. Much easier to forego the personal connections and use a pseudonym. When I had two pieces published under the pseudonym, it was an especially satisfying experience, since it was based on the apparent quality of the writing, not on the personal connections. And I never let those editors know that was me. Payments were made to my company, so I have never been found out. It's kind of fun living a double life.
On the other hand, it seems that so many people here are teachers who write horror and smut. That says something about you teachers! Hell if I'd let you anywhere near my kids (just kidding...I think). There is a solution to the problem, exclusive to teachers. It's called "tenure". Get that, and you can write all the gory sex novels you want, and they can't fire you.