Jews for/against Jesus

Hmmm. There are some questions that are dangerous to ask, but I must. The thing I can't understand is: What's all the saltiness about Y'shua? The only reason I bring it up is because I happened across this morsel in the NYTimes [From Jews for Jesus Hit Town and Find a Tough Crowd]:

''This is not Jewish versus Christian,'' said Craig Miller, who works in the antimissionary arm of the Jewish Community Relations Council of New York, called the Spiritual Deception Prevention Project. ''It's about deception pure and simple. The groups that are coming are bringing a deceptive message that one can be both Christian and part of the Jewish community.''

Is it really like that? I thought--and maybe I'm wrong--that people are born Jewish as in, even if you don't go to synagogue, you're still a Jew. I used to hang out with a Messianic Jewish guy, who has since relocated to Israel, and his congregation was, well, Jewish. Most of the Jewish kids I knew in high school were secular but I don't think any of them ceased identifying as Jews.

If a person of Jewish descent chooses to follow the teachings of Y'shua do they then cease to be Jewish? If so, how and when? Or is it just if they refer to him as Jesus? ;0) Anyways, I figure since the internet is such a big, gianormous place full of random people from which I can extract answers, have at it! I'd really like to know.

[A general statement: I can understand that some Jewish folks might feel a little uneasy being identified with Christian folks because of bad history on the part of the Christian church-at-large ie., let's use Christ's crucifixion as an excuse to execute millions of people - Hitler. I just don't get the logic of the sentiment against Messianic Jews.]