I think Christianity is a fine religion for non-Jews, the best of all available alternatives, to my knowledge. The reason Jews don't attempt to convert others, and in fact discourage conversion, is that the essence of Judaism is choosing virtue of one's own free will. While we may disagree on specifics of doctrine, the essence of Christianity is very similar. So I guess what I am saying is that Christianity is essentially a vehicle for bringing the lessons of Judaism to non-Jews, which accords with its historical development.
This is a common misconception among Jews.
It is true that Judaism is not missionary in the sense of requiring non-Jews to become Jews (since the Jews are a small nation with a special national covenant with G-d). However, Jews are charged with converting all non-Jews to the Seven Commandments of the Sons of Noah, and these commandments forbid not only murder, theft, and sexual misconduct, but idolatry as well. Now I realize that there is a lot of Halakhic discussion as to whether or not sincere chr*stians are idolators, but idolatry or not, chr*stianity is simply false, and one is always better off by knowing the truth.
Moreover, the non-Jew is obligated not only to accept the Seven Noachide Laws but to do so specifically on the authority of the Torah which G-d gave to Moses and Israel on Mt. Sinai, and not for the rationality of the laws themselves.
RaMBa"M in the Mishneh Torah actually says that Moses was charged with confronting every single non-Jew with the choice of conversion to the Noachide laws or death--a task that I suspect will actually be fulfilled during Milchemet Gog uMagog.
This isn't exactly what most Jews think their attitude towards the non-Jewish world is supposed to be, but, as I understand it, this is the true Torah position. What many Jews fail to understand is that the attitude that "hey, it doesn't matter which G-d/"gxd" you believe in so long as you're a good person" is absolutely incomprehensible to their Evangelical "opponents."