Karol Wojtyla taught that in making an ethical decision, a moral agent does not only give rise to a particular act, but he also contributes to the person he is becoming. Every time I perform a moral act, I am building up my character, and every time I perform an unethical act, I am compromising my character. A sufficient number of virtuous acts, in time, shapes me in such a way that I can predictably and reliably perform virtuously in the future, and a sufficient number of vicious acts can misshape me in such a way that I am typically incapable of choosing rightly in the future.
This is not judgmentalism. It is a kind of spiritual/moral physics, an articulation of a basic law.This is something he applies directly to engaging in acts of casual sex. That is that they compromise your moral character. This is something you don't hear very much about. That sexual immorality will produce other forms of immorality. Conversely that being sexually pure will make you better morally in other areas of life.
This is something many people assume is false. When Bill Clinton does something sexually immoral nobody says that that makes all his moral judgements suspect. People assume that is just one area of life that won't affect his job, even such a multifaceted job as president of the US. They talk about Kennedy who committed adultery a number of times. He is considered a saint by American civil religion so he can't be questioned.
Even in today's paper there was a headline that struck me. A person on trial for child pornography was charged with murder in an "unrelated" case. That seemed like a loaded word to put in a headline. How do you know the moral problems he has in the area of sex are unrelated to moral problems in other areas of life? I do remember reading about some study that showed exactly the opposite. That people who indulge in porn do commit more crime. That is violent crime, not just sexual crimes.
I find that even many Christian resources don't make this argument. They say your sexual choices impact your relationship with God. That might in turn effect your moral life generally. But the idea that even for non-Christians and even for people that don't believe something is immoral. Just the fact that what they are doing is against the moral order will cause their character to degrade.
So even if you honestly think there is nothing wrong with hook ups or pornography or artificial contraception just the fact that it is wrong means your entire moral life will suffer if you engage in it. The "acts can misshape me in such a way that I am typically incapable of choosing rightly in the future." Certainly if you know they are wrong and do them anyway the effects will be worse. But simply getting rid of all teaching on the wrongness of such things does not solve the problem. The wrongness is inherent in the act. Our conscience will tell us that on some level at least for a while.
Those of us whom God has entrusted with the knowledge of that wrongness should say something as well. After all, evil won't stop when it infects the whole person. It will infect the whole of society. Unless people start saying they don't want to live in that kind of society. But so many of those people have been misshaped by what was considered casual sex 30 years ago. Not as bad as the hook up culture today but a long way from a truly moral sexuality. Back then 3 sexual partners a year was considered casual. Now it is more like 30. So we are getting worse. Most of today's parents have not had a solid moral formation so they can't provide one. Really a return to the church is our only hope.