It's not about whether it's right or wrong. There may well be a lot of truth in it. The Old Testament simply doesn't apply to Christians.
I wouldn't dream of challenging any Jewish person on their faith.
By being a Christian you are challenging every other faith. That's the point, these religions don't say "Ours is right but others are too" because that wouldn't make sense. If you grew up in Iran you'd have been a Muslim, surely? In which case, even if you are right, then you are right by circumstance and chance.
I find the whole thing quite bizarre, to be honest, but as you say, each to their own.