I'm a christian, I would love the bible verse for this
Actually, this is true; you can find examples of polygamy and prostitution in the Bible. I don't know verses, but I'll list some folks from the Bible that you'll recognize:
Abraham -- married to Sarah, took her handmaiden as a second wife to have a child
Tamar -- disguised herself as a prostitute to trap her father in law (was it Judah?) because he wouldn't fulfill his family obligations to her
Jacob -- married both of Laban's daughters, Rachel and Leah
David and his son Solomon -- sort of the playboys of the Old Testament, these two each married many women (Solomon had 1000 wives; well, some were concubines, but the point is still valid), yet David is called "A man after God's own heart"
Rahab -- prostitute who hid Jacob, then helped him and his fellow spy escape the city, was an ancestor of Jesus . . . however, the Bible also mentions her faith, so I suppose she changed her occupation and we can take this as a story of redemption
However, every one of these examples is from the Old Testament. I cannot give a single example of a multiple marriage from the New Testament, which seems to be an indication that society was evolving away from that idea. In fact, Ephisians gives specific instructions on how husbands and wives are to treat one another, and those verses use singular nouns and pronouns -- not plural, which also indicates that multiple marriage was no longer considered appropriate.
You could also make a strong argument about "then vs. now" using Sociology and Anthropology rather than the Bible itself: In the Old Testament, society was nothing like ours today. Slavery was accepted, though it wasn't anything like slavery in America so many years later: Many slaves were essentially like us middle-class folks today, working for someone else. The focus of the entire family was the oldest son; he would inherit half his father's wealth, but he'd also inherit the responsibility of continuing to care for his father's wives, any young children the father left behind, his business, and his servants -- he couldn't turn down this responsibility. And clearly their society cared about providing protection for unmarried/widowed women -- a woman on her own was really in dire straits; they had rules about leaving so much grain in the fields for man-less women to gather, they had rules about a younger brother siring a child with his widowed sister-in-law, they had rules about providing for elderly and childless widows. Today a single woman can provide for herself, so those rules aren't needed.
Anyway, it's really not fair to look back at those days and say, "This is okay because you can find examples in the Bible". That'd be cherry-picking one detail from their society and trying to transport that one item into modern-day life. That just wouldn't work in the big picture -- you might just as well say that we are still required to take blood sacrafices to the high priest in a temple.
