could it be that they're not worried about impressionable youngsters, but about blurring the line between Jews and Jews for Jesus?
there's a reason why people get much more worked up about Messianics than they do about BuJews. it's called History.
Agreement with both of yous. I'd freak out over Jewish-by-ethnicity Christians inserting themselves into any kind of Jewish-religous context. But why not just open the Chidon haTanach to everybody? It'll be more exciting that way, with tinges of religious warfare and Eliyahu-on-the-Karmel and all.
I agree with Steg. I think the issue (rightly or wrongly) is fear of being seen to legitimate Jews for Jesus as a mainstream part of Judaism.
ADD, I know you like being a contrarian, hence the names of the blog. I respect that. Really I do. But Steg's point, which I was about to type before I saw that he beat me to it, is so obvious, that...well...
Oh, were you looking for a clever way to throw in that last word? That was good. 
Adderabbi: Just as an aside, how would you feel if it were a Gemara contest? Do you think it would be appropriate to be open to all?
I agree that the point I think Yad L'achim is trying to make is to not legitimize JfJ as part of mainstream Judaism.
Honestly, I would have no problem with the disqualifying Chabadniks who outright say that the Rebbe is Messiah/god
Why would you have a problem with that?
I respond to many of these questions and arguments in a more recent post.
Also agree with Steg.
But you have the best (and funniest) last word.
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