What would be a good counter arguments to this idea?

[**Sex Before Marriage Is Not A Sin**](https://cluecho.com/8834/uncategorized/sex-marriage-not-sin/) I found this article that says that sex outside marriage is not a sin. Some samples are > Ruth and Boaz > > Really? Where does the Bible give a green light to premarital sex? > Perhaps the most striking example is in the story of Ruth, though > there are other examples as well. According to the Book of Ruth, when > the recently widowed Ruth and her mother-in-law Naomi were faced with > a famine in Ruth’s homeland Moab, they returned to Israel impoverished > and with little hope of survival. Ruth took to gleaning in the fields > to find food for herself and Naomi. The owner of the fields, a > relative of Naomi named Boaz, saw Ruth and was pleased by her. When > Naomi heard about it, she encouraged Ruth to adorn herself and > approach Boaz at night while he was sleeping to see what would happen. > Ruth took this advice, resting with him until morning after first > “uncovering his feet” (in Hebrew, “feet” can be a euphemism for male > genitals). The next day, Boaz goes to town to find out whether he can > marry her, and, luckily, another man with a claim to Ruth agrees to > release her. They do marry and together they produce Obed, the > grandfather of King David. > > None of this would have been possible if Ruth had not set out to > seduce Boaz in a field, without the benefit of marriage. [The Bible’s Contradictions About Sex](http://www.bu.edu/articles/2011/the-bibles-contradictions-about-sex/) Another is David and Betsheba. It's not a sin because Batsheba is not technically married. [David and Bathsheba](https://torahideals.com/essays-and-imaginings/david-and-bathsheba/) says it's not sin at all. Yet, not having sex outside marriage seems like the most talked about rules in christianity second only to believing Jesus is God. So what would be a good counter-argument? Also is there reasonable reason to say that this is very open to interpretation and that the bible is simply not clear about the idea? Is it okay to say that, yes it's sin and no it's not a sin is well within possible interpretation?