I’m not so sure how true that is, actually. Jesus offended the establishment so much that the Romans executed him. He was certainly an iconoclast. Paul was equally unafraid to say unpopular things that got him in a great deal of trouble with the Roman authorities.
I’ve never seen any evidence that early Christians opposed things like slavery and the traditional legal oppression of women. I suspect your friend’s argument is more wishful thinking than anything else. I mean, it would be nice to believe it, and it could be true. But is it true? Nothing in the New Testament or early Christian writings that I’ve ever seen would support the premise.