Excellent point. So why is it that every Jew who comes to that realization (that Jesus is YHVH manifest in the flesh) is immediately rejected by the whole of Judaism and is no longer recognized by Jews as being a Jew?
Or do you believe that there is such an animal as a Jew for Jesus, or a Messianic Jew?
And if there is, then why is Israel so adamant about prohibiting the Jews for Jesus people from proselytizing Jews in Israel? Aren't they (according to your definition) just Jews who believe in Jesus?
You can be an atheist Jew, you can be a Zen Bhuddist Jew, but it seems that you can't be a Christian Jew? Am I wrong?
Technically speaking, a Jew who ceases to practice Judaism remains a Jew. He might be considered apostate, but he would not need to "reconvert" if he changed his mind and wished to return. When people say "he is no longer Jewish", they are either speaking in error, or referring specifically to his religious practice.
With regards to why Jews react so vehemently when a Jew becomes a Christian, I think there are two factors to consider. First, there is the almost 2,000 years of history to consider. Up until fairly recently, Jews suffered a good deal of persecution at the hands of certain Christians. It may not be fair for Jews today to hold this against Christians today, but it is a reality. And unfortunately (as a quick google search would reveal) there remain some self-professed Christians today who continue to hold anti-semitic beliefs.
Second, it is a matter of religious identity. Every religious body has the right to define what it means to be a member of that group. If I strongly held beliefs in free will and conditional salvation, I wouldn't fit in well in a Calvinist church. If I rejected the teaching authority of the popes and the bishops, I wouldn't really be a Catholic. And so on. Central to Jewish belief is that God is One, indivisible and unchangeable. Beliefs such as the trinity and the incarnation, as defined by orthodox Christianity, just don't fit into Judaism as Judaism defines itself. Conversely, orthodox Christians would probably say that a person who is a unitarian or a tritheist is not really a Christian.
Or do you believe that there is such an animal as a Jew for Jesus, or a Messianic Jew?
They exist. How they choose to define themselves is their own decision. Whether or not other Jewish denominations wish to accept them is their decision.
And if there is, then why is Israel so adamant about prohibiting the Jews for Jesus people from proselytizing Jews in Israel?
I don't know what the specific motivations are. I do know that many Jews object to the tactics used by certain messianic groups.
You can be an atheist Jew, you can be a Zen Bhuddist Jew, but it seems that you can't be a Christian Jew? Am I wrong?
Again, it depends from what perspective you are looking. From the standpoint of birth, all of the above would be Jews. Orthodox Judaism would see all of the above as apostate. And both Conservative and Reform Judaism define themselves differently than Orthodoxy.