I'm the one who said the evangelical church world has a major problem in this area.
However, I can't agree with “zero difference.”
We also need to clarify our terms.
“Professing Christians” would include everything from “Christmas and Easter” people who aren't even on the membership rolls of a church anywhere to people in high-commitment congregations with a strong emphasis on personal conduct.
We also need to deal with the reality of repentance from sin. There's a huge difference between two young people in a lukewarm supposedly evangelical church who decide to go to bed and don't think it's that big of a deal, and a woman in college who has “been around” and has a radical conversion which results in a firm commitment not to be sexually involved with anyone else until marriage.
I realize it is impossible to statistically measure personal faith. However, church attendance is a statistically valid measure of the externals of personal commitment. It's not perfect, of course — we all can talk about people who have legitimate reasons not to be in church — but it is statistically valid.
You would find major differences in rates of promiscuity, as defined by multiple sexual partners over a designated period of time, and the rates of premarital sexual activity, if the general American population were compared to those who attend church or synagogue weekly or more often and did so during the period of time when pre-marital and non-marital sexual activity is being measured.
It started with the Age of Reason and escalated with the French Revolution and rise of communist/anarchist writing. Pope Pius IX warned Catholicism in the Syllabus of Errors, as did many of the great 19th century Evangelicals.
The Russian Revolution and subsequent rise of totalitarianism SEEMED to be a wake up call for western civilization, but it really wasn't, C.S. Lewis saw this and warned that secular humanism was the greatest threat we faced.
In the past fifty years, we have seen Christians embrace all forms of humanist heresy. Nonsense that would have been unfathomable (same-sex "marriage", abortion, etc.) a century ago has increasingly become the norm.
So yes, it is not surprising that young people who call themselves Christians engage in premarital sex. The ONLY thing young people are typically taught regarding sex is that it must be "safe."
But, in spite of all of society's pressures to the contrary, I have noticed an increase in young people embracing traditional Christian morality in the past ten to fifteen years. They have seen a generation lost to abortion, they have seen the destroyed and empty marriages of their parents and grandparents and they are finally awakening to the realization that God's plan is the only one that will result in an abundant life.
Drive around on a Sunday morning and you will SEE the churches where the true Gospel is being preached. You will know these churches because you will see young families with children who WANT to be there, you will see teenagers who look happy (and are dressed appropriately). These are the same people that we saw several weeks ago in Chik-fil-A who were happy to wait up to an hour in a crowded restaurant just to show Chik-fil-A that people really do care. So yes, true Christians are all around us, we just have to open our eyes and see them.