well, there I’ll have to part ways with you. Jews for Jesus is attempting to convince Jews that Jesus was the promised Messiah, in other words to become Christians. So it’s mutually exclusive with being Jewish to be a Jew for Jesus. But other than that, I don’t think Jews object to them any more than they do to any other attempts to proselytize.
The early Christian church was almost exclusively Jewish, then began to include Jewish proselytes (who accepted Jesus as the promised Messiah), then, finally, after much debate, it was agreed that Gentiles (non-Jews) could join the church. So there is no contradiction between being Jewish and being Christian, it is just that many don’t understand today that there is a New Covenant that God has made with Abraham’s seed (Jews) that supercedes the Old Covenant. Many Jews rejected the New Covenant in Jesus’ day, but many accepted it. They also don’t understand that God changed Abram’s name to Abraham (meaning father of many nations) or the fact that Christians are also Abraham’s seed by faith: GAL 3:29 “And if ye be Christ’s, then are ye Abraham’s seed, and heirs according to the promise.”