For many years, my faith hinged on the bible. It was the one true source of authority for what was right and wrong, and the people who surrounded me believed that, too. Using the bible was the best way to defend yourself in an argument, because one verse was enough to defeat countless arguments for another position, no matter how well-founded they were as long as they were not also from the bible. As a result, people rarely challenged widely-accepted interpretations of passages of scripture. It could appear as though you were trying to twist the words to your own desires, and even worse, people would assume you were only trying to defend a sin you must be already committing. In a Christian community where you are constantly being judged as "one of them" or "someone who needs to change before they are right with God," being assumed to be sinning was an embarrassing and isolating experience.
That is one reason why no one ever really challenged our "biblically-based" beliefs on premarital sex, as well as masturbation, pornography, drugs, or homosexuality. Less-embarrassing potential sins were debated openly and freely, like tattoos, dancing, alcohol, gambling, or swearing.
I myself never questioned the biblical basis of my beliefs on sex because it was so in line with everyone else that no one ever asked me to defend it. Any sex outside of marriage was wrong, period. It wasn't until I started questioning the negative side effects of purity culture that I began to wonder if the whole foundation of it (the biblical interpretations) were wrong.
Basically what I found was that there were no verses in the bible that specifically condemned premarital sex. There are many verses that speak against "sexual immorality" and sometimes "fornication," but if you look deeper you will find they are translating from the greek word porneia, which is debated to mean other things--not premarital sex, or even the catch-all term "sexual immorality."
I wondered at first why most Christians assume premarital sex would fit in the category of sexual immorality. Of course, most believe it because their culture has always believed it. When questioned, they can come up with a lot of negative possible consequences of sex, which is enough for most people to declare a blanket decision on the question, even though most of those consequences are from non-consensual or unsafe sex, or involve people with evil intentions. No exceptions are made for all the other kinds of sex being had in the world. Then there is the issue of Old Testament laws regarding sex, which are very harsh. Even though many Christians will agree that the old law was done away with when Jesus fulfilled it in his death, they still like to use it as backup if it aligns with their position.
I do think that most of American Christianity's beliefs about premarital sex derive more from culture than from the bible. American culture still demonizes sex and is uncomfortable with it. We can't help but assume it is what Paul was talking about in his letters. Forget about the difference in cultures 2,000 years ago, historical context and the art of translating ancient languages! "The bible is clear on this issue..." Now that only makes me laugh. "I'm just following the bible" is another weapon pulled out from time to time. But it doesn't fool me anymore.
As you might have guessed, my faith is no longer solely based on the bible. I do not believe the bible is inerrant anymore. I doubt that every author in it was "spirit-led" at the time. But I still hold it in esteem and understand that there are people who need their beliefs to be defensible via scripture.
When it comes to biblical interpretation, there is a lot of bullying that goes on, in the form of mocking outliers, making accusations regarding the motivations of questioners, fear-mongering, and creating community divisions. I want to encourage Christians who trust the bible as their only authority on faith to be bold in asking questions and challenging norms and to see that people who do not see premarital sex as a sin can make a good biblical case, too.