You suggest that we separate between ethical teachings and the more intolerant aspects of religion, and I respect that. If more people took your view, people of different faiths might start to converge. Take the teachings of Hillel and Christ mentioned above. Hillel says that we must not do bad deeds and Christ says that we must do good deeds. The two ethics are similar: the Christian command “be kind to your neighbor†could be translated to the Jewish commands “don’t walk your dog on your neighbor’s lawn,†“don’t blast the stereo after 11 pm,†etc. The Christian ethic perhaps allows for positive acts of kindness, such as charity and self-sacrifice, in a way that the Jewish ethic doesn’t, while the Jewish ethic has greater specificity and clarity. Each of the two codes of behavior is incomplete by itself and a person could benefit by adhering to both.
I would add, however, that your belief that Christ is not the messiah, or that this belief is a later amendment to Christianity, is your private faith and not representative of your religion. Messianism was introduced by the Hebrew prophets several centuries before Christ. Isaiah, Ezekiel, and others foretold of an anointed one of the Davidic line who would bring about a resurrection of the dead and usher in an age of everlasting peace and prosperity called “the world to come.†This promise of a golden future was a nice way to keep Jews from despairing and abandoning their faith as one foreign power after another conquered Jerusalem and defiled the Temple. Then Christ came along and proclaimed himself the messiah. The Jews rejected his claim. For one thing, Jews don’t believe in an afterlife – this goes back to ancient Judaism’s abhorrence of the Egyptian and Canaanite cults of the dead; in contrast, Jahweh had no relationship with the dead – and Christ was saying that he first had to die in order to return as the messiah. Reread Christ’s sermons, Father Tim! Don’t make me quote all the passages that read “I will come like a bolt of lightning from east to west,†and “I say to you sinners, it would be better if you had never been born.†Already twenty years after the crucifixion Paul was busy contriving Christ’s genealogy to David and preaching that the world would end in his own lifetime, a claim reiterated by all the church fathers till, around the fourth century, Christians became skeptical that the Second Coming was imminent and postponed the event indefinitely. The Nicene Creed of 325 which you cited doesn’t even mention the messiah, but the Constantinopolitan Creed of 381 “looks for the resurrection of the dead, and the life of the world to come,†ideas which, believe me, weren’t invented there. It is unimaginable how differently history would have played out if Christ had settled for being a great teacher instead of the messiah.