A woman once wrote to Miss Manners (aka Haragamam) with a story 
about a man she had sat next to on a plane trip. In the story, the man had asked her, “Are you a career girl?” What should she have answered? asked the woman. Miss Manners answered that she was perfectly within her rights to answer in the affirmative (since she was indeed a “career girl”) and, in the spirit of friendliness and reciprocity, ask the man if he was a “career boy.”
I’m all for turning the tables on people who ask jarring questions. And one of the silliest questions I and other converts to Judaism are asked is, “Why would you convert to such a nutty religion?” If the asker wants to discuss the ways in which Judaism is nutty, well and good; I can partake. But if the question is really just a thinly-veiled insult (another way of saying, “How could you have been so stupid?”), a snappy answer may be called for. Here are a few responses to consider for those who want to answer the question in the same spirit:
1) because the Jews have all the money;
2) because the Moonies rejected me;
3) because Jews control the world. Just read the papers;
4) because the Scientologists are too nutty, and the Unitarians aren’t nutty enough;
5) because I heard Jews aren’t supposed to ask nosy questions.
One can also ask the asker, “Why would you ask such a question?” After all, why a convert did what she or he did is not anyone else’s business. (This retort also works for people who ask if your triplets are “real,” how much money you make, and why you don’t cover your hair. Thanks to Heather for the tip on this one. Another Miss Manners response, I believe.)
Of course, one is always welcome to plumb the depths of one’s soul and come up with a real answer if the asker is someone with any right at all to know.
But I have a fourth way to deal with this situation. Converts or potential converts should try asking born-Jews why they stayed Jewish. If they think it’s so nutty, why don’t they convert to something else? Bet they haven’t thought about that one. (If you get the opportunity to ask this question of a born-Jew who has opened the subject, please come back and write about what happened.)
How do you think one should answer a question like this?
Shimshonit 
Usually by stuttering and saying something honest and none of their business. I have to learn to answer rudeness with rudeness.
The times that I have asked converts why they converted to Judaism, I’ve always presented it in the following way. First, I actually ask a more focused question, which is “What attracted you to Judaism?” That’s really the question I’m most interested in knowing the answer to, which is, what made Judaism appealing.
Even before I ask that question, though, or sometimes just after I ask it but before I expect the answer, I explain that I doubt I would have converted to Judaism had I not been born into it. And I explain that what I find attractive about Judaism are its emphasis on the here and now and the tendency toward rationality I find within it.
Of course, the first thing I do is ask the person if they would mind a personal question. :-)
I applaud anybody who converts but do understand the person who asked why you would convert. If you are born Jewish you spend your life meeting non-Jews who always give you an “aaah” and then a pause when they hear you are Jewish. Old hatreds die hard and the world was anti-Semitic for a long time and still is. When I say I am Jewish to a non Jew who does not live in a big city, out there in the mainly Prostestant middle of this country, it is as if that person is now taking a second look at me to make sure I am all right, no horns, nothing centuries of lies have literally been ingrained into their psyches. When the man says “all that crap”, he means the looks, the jobs you perhaps will not get, or the tough time you might have on a job if you are Jewish. Years ago I went to work as an R.N at the Brooklyn V.A Hospital and the first thing the Irish head nurse wanted to know was if I was Jewish or if I was only married to a Jew. It was my first known brush with anti-Semitism. Then she proceded to make my life miserable and I didn’t even know it was because I was Jewish till some other staff nurses on the floor took me aside and told me to stay out of her way because she hated Jews. This was about 30 years ago but neither was it 100 years ago either. My children experienced much more anti-Semitism than I did as we lived in a mixed neighborhood when I was raising them as opposed to the totally Jewish neighborhood I was raised in. That’s why the man asked you the question. He meant why would you subject yourself to, well literally, the Jewish stigma. Sad, but true. He was being honest.
I think you’ll find this post of interest:
http://mabfan.livejournal.com/427698.html
My answer to the flip-around question:
Because I believe that the Jewish World View – 613 mitzvot for Jews, 7 commandments for everyone else – is the way to go. With my life experience to this point, as much as I can imagine what I would do if I had been born Jewish, I think that I, personally, would choose to remain a Bat Noach, observe the 7 Noahide laws to the best of my ability, and be supportive of Am Yisrael in whatever way possible. But I do not think I would choose to convert. However, as somebody born Jewish, I believe that I am obligated to remain so; I do not think it is permissible (for me) to convert OUT. Based on my own perspective and experience through this point in my life, I do find it somewhat baffling that someone would choose to convert IN.
Depending on my relationship with the person, and whether the reason is obviously (such as already being in a relationship with another Jew), I may bring it up (as politely as possible, of course).
Heather: Or not. It’s the ideal not to be rude, even in response to rudeness. You’re probably doing the right thing, though being at a loss for words doesn’t help. I always thought it was the non-Jews who were supposed to give us a hard time…not the Jews themselves.
Michael: You’re always nice about it. Not everyone is, though I think the ones who are less polite are the ones who don’t understand Judaism the way you do. I agree with the here and now; would that rationality include kitniyot? (Just kidding here…) I enjoyed your post on this subject–thanks for the link.
Eleanor: Though one likes to think of the world as progressing toward a state that is more civilized rather than less, anti-Semitism is still alive and well, with anti-Semites becoming less and less abashed about their hatred. I sometimes think we’re on the verge of returning to the 1920s, when anti-Semitism was ingested with one’s breakfast cereal, and even fashionable. The most upsetting brand for me is that of non-religious Jews who see their own faith as backward and Israel as an embarrassment rather than a triumph. Seen through that sort of lens, I suppose questions of why one would convert make sense. But no convert goes into this blindly; the beit din is supposed to make clear that Judaism is not a popular choice of belief in this world (in case the potential convert has missed that memo). It takes a pretty true set of beliefs to overcome that fact, but Judaism triumphs with heartening frequency.
Shanna: I hear what you’re saying. Many born-Jews are too close to it all to see it from the same perspective as an outsider. I do occasionally meet up with people born Jewish who can step back and distance themselves from their beliefs and practices to see both the beauty and the nuttiness of their religion. Can’t be easy, though.