I think most people would like to learn a foreign language. I'm sure that we've all contemplated learning a language, and many of us have actually done it!
In Public Schools in America, very few of the ESL teachers can actually speak a foreign language. Which is surprising to say the least!
I would think that teachers who can speak a foreign language would have better insight into the language learning process, thus have innately and inherently better ability to teach ESL.