I don't really see the issue. We can argue for eons about whether, say, Judaism is "right", but there are facts involved. You can't make a pig kosher, you can't make Vishnu not a Hindu god, you can't make Christians not believe that Jesus is the Messiah. And along the same lines, you can't say Jesus is the Jewish messiah. The people who get to decide who the Jewish messiah is are Jews. The fact that Christians believe that Jesus is, in fact, the Messiah doesn't make him the Jewish messiah, it makes him the Christian one. They now have their own set of terms and definitions. Christians don't get to dictate the terms of Judaism, just like I can't tell a Muslim what the Koran says.
I'd have NO problems whatsoever with Christians if they could manage to say, "From a Christian perspective, this is true," but they don't-- they keep insisting that they have a better, more complete understanding of Judaism and Jewish thought than do actual Jews. "It's in the old testament, you should agree with me!" "Jesus WAS the Jewish Messiah, if you knew your scripture you'd agree with me!" : Come now. I'm not saying "Stop believing in Jesus, stop calling him 'Christ' or 'Messiah,' if you had read your own scripture you'd know you were wrong." Just the opposite-- from your perspective, it may be true... but if you're going to call him the Jewish Moshiach... well, you're just wrong. And you're never going to be right about that. That's right, I'm saying it-- if you're a Christian who "knows" that Jesus was hte *Jewish* Messiah, you're wrong.
It'd be like... well, like the manager of a Walmart trying to tell the CEO of Dell how to do his job. It just wouldn't make any sense.