This seems to be a common talking point among people who don't know much about Christianity. Orthodox Jews still live by the Old Testament, so maybe you want to try that gimmick out on them.
Christianity states that the coming of Jesus and the New Testament(aka the new covenant) replaced the Old Testament(aka the old covenant) given to Moses by God. It replaced the Mosaic Law with the Law of Grace.
That's why Paul wrote this:
"...who made us adequate to be servants of a new covenant not based on the letter but on the Spirit, for the letter kills, but the Spirit gives life..."
"For indeed, what had been glorious now has no glory because of the tremendously greater glory of what replaced it..."
And also here, where Paul explains that the Mosaic Law was meant to be a temporary guardian until the coming of the Messiah:
"Thus the law had become our guardian until Christ, so that we could be declared righteous by faith...
But now that faith has come, we are no longer under a guardian. For in Christ Jesus you are all sons of God through faith..."
I'd suggest reading a little of the New Testament and studying up on the basic tenets of Christianity before bashing it and embarrassingly displaying your ignorance.
Wrong. Jesus only did away with the Ceremonial Laws (ie sacrificial laws, since he was the final sacrifice). He even said himself that none of the other law shall change ("not one jot, nor tittle..." or some shit like that) from the rest of the laws. Dietary, Criminal and Civil laws remain.