Christians, Messianics, and Jews
First, I have to confess that I can understand and relate to several points he has made stating that Jews themselves define what Judaism is, and it excludes those who worship a man--even the God-Man. So, in other words, the prevailing argument is that Messianics are not Jews.
However, I would like to propose that what is meant by Messianics and Christians by the term "Jew" is not the same definition as what an orthodox Jew might mean, and as such, if we can dissect the issue there may be less of an argument.
Messianics (and all Christians who actually understand orthodox theology... probably an equally minor proportion as in Judaism) understand that what it means to be Jewish is to be an Israelite in covenant with the One God wherein, among many other facets, sins are forgiven by expiation through a sacrifice.
If in fact Judaism and Christianity can agree up to this point, then the key difference is not in whether a person follows Jewish interpretation of the covenant--or rather, an acceptable New Covenant as described by the Prophet Jeremiah--but whether their interpretation is in fact one Jewish interpretation.
At this point, it's prudent to point out that there is a varying viewpoint on theology even among those who call themselves Jews today--ranging from orthodox to apostate.
So, the fact remains that a few Pharisees (Paul & Nicodemus), a zealot (Peter), a Rabbi (Jesus), and several fisherman and carpenters who were all themselves Jews were the originators of this new, albeit unorthodox, interpretation of the Hebrew scriptures which undergird Christian theology and Christology. So, is the Jew with a View right in claiming that Messianics are not Jewish? That they have no claim to the name "Jewish?" I don't think so.
If by this point in reading this post you're entirely lost... I would encourage you to read up on the arguments made at http://ajewwithaview.wordpress.com and, if you are so inclined, join the discussion!