"In an arrangement sanctioned by Jewish law, according to these opinions, the woman becomes a pilegesh, or concubine. Neither the man nor the woman has any obligations or rights, but both must adhere to family purity laws in accordance with Halacha."

Huh...? I'm supposed to be a religion scholar, but this kind of mystifies me. The availability of a mikva removes one of the major obstacles to premarital sex? What about the commandment against adultery? That doesn't count?

Although this seems to have been forgotten in the popular mind, adultery does not actually mean sex between people who are not married. It means sex between someone who is married and someone who is not his or her spouse. Originally, it meant sex between a married woman and a man who was not her spouse. In any case, a commandment not to commit adultery had no impact on a couple where both partners were unmarried.