Well, then I’m a-gonna haveta pick back then! 
As I just recently said here: I hate this debate. (but somehow this doesn’t stop me from jumping in with both feet)
It never goes anywhere (and that’s not intended as an insult, andros, but…)
Yes. I will conceed that the dictionary does define Jew as both ethinicity and religion. And I understand that the dicitonary doesn’t define words, it reports useages (ie: There’s no sinister cabal of lexographers dreaming up new definitions) but…
Jew as an ethnicity is meaningless. It’s primarily used by
four main groups.
A) anti-Semites who are trying to pretend that there’s a genetic difference between Jews and “real men” (Miss Creant’s “horn and tails” comment referred to this.) Nazis were also big on this useage. (Not a Godwin’s Law reference! I wasn’t calling nobody nuthin’!
)
B) Non-religous people from Jewish families using the word to describe their background. They have the right to use the word Jew, but I don’t agree with them. They don’t agree with me. Both sides annoy each other, in a more-or-less family-like way. 
C) Phoney counterfits like “Jews” for Jesus, claiming that they’re real (“fulfilled”) Jews, the rest of us being just “ethnic” Jews.
D) Otherwise well-meaning people who don’t know better.
There are other reasons the term is used, but in my experience, the vast majority of people using the term “ethnic Jew” fall into one of the above catagories.
To me, of the four arguments I listed, only B “My parents were Jewish, and so I’m a Jew, but an athiest one” has any legitimacy to me, but this (ongoing) arguement feels (to me)like what vegetarians must go through:
“I’m a vegetarian. I eat vegetables, and I only eat fish sometimes.”
“Fish isn’t a vegetable. You’re someone who eats a lot of vegetables.”
“I am so. I’m mostly vegetarian.”
“No you’re not. It’s an either-or proposition.”
“Besides, fish are cold and slimy and icky, so it’s ok”
::vegetarian kills him/herself:: 
I understand that non-practicing people of Jewish background feel that people on my side of the argument are being equally…um…hardheaded? 
In any event, really, look at the definition you listed:
“A member of the widely dispersed people originally descended from the ancient Hebrews and sharing an ethnic heritage based on Judaism.”
Widely diverse people sharing an ethnic heritage…either “ethinic heritage” means “religion” or it’s a meanless term. What “ethinic heritage” other than religion does a Jew from Yemen share with a Jewish Israeli soldier or my converted-Jewish, Scottish, cowgirl sister-in-law? Not skin color, not history, not line-of-descent. Only religion.
Fenris