During a 2011 roundtable discussion on Fox News, guest commentator Jay Thomas argued that young people should not be too concerned when it comes to pre-marital sex, because nobody would choose to "buy a car without driving it first. You don't get married, and you don't learn about sex, by not having it." Any reasonable person would prefer to avoid someone who might be, in his words, "odd in the sack," much as any reasonable person would prefer to avoid getting a lemon when purchasing a new car. Mr. Thomas, therefore, could hardly envision anyone's committing to marriage without first "kicking the tires" a bit, and going for a sex "test drive."

The test drive analogy comes up short in a number of important ways, and premarital sex is not at all synonymous with a harmless "test drive." The context in which sex occurs is everything in terms of "getting it right." Separated from its proper context of marriage, it becomes a quick path to emotional and interpersonal wreckage. Since sex takes on its proper meaning only within marriage, it cannot be properly evaluated outside the marital commitment. It might be analogous to trying to evaluate the performance of a particular car before it has even been assembled or come off the assembly line.

The story is told of a famous but irresponsible race car driver who decided to borrow a friend's Camaro to take it for a test drive around the racetrack. He quickly ran it to the edge of the speedometer, red-lining the engine at over 100 miles per hour. He pushed it hard for several laps around the track, then finally pulled the vehicle off to the side. As he did so, the strained engine overheated, seized violently, and began to pour out smoke. He was used to expensive, high performance racing machines, and the Camaro felt sluggish by comparison. He walked away from the vehicle, muttering under his breath, "I wonder what's the matter with that car?" Sex before marriage is a similar kind of "test drive" -- clearly unreasonable and harmful.

A sexual "test drive" mentality is essentially exploitative in nature, reducing a potential spouse to someone who is easily replaced by a "better" model. When we take a car for a test drive, and don't like it, we can just return the keys and move on to the next model. But people are not cars that we can just exploit and cast aside.

The notion of a sexual "test drive" as an entree to matrimony trivializes and degrades the serious business that marriage really is. What sorts of things would a young man be expecting to discover with a sexual "test-drive" anyway? What kinds of qualities would disqualify someone from becoming his wife? If he had lived in purity himself, and it were his first sexual experience fresh on the heels of his marriage vows, he would automatically suppose his wife to be wonderful, and no "comparisons" should even be necessary.

In the final analysis, who really wants to be sexually "compared" to others anyway? Predictably, partners can feel threatened if they think their spouse might be comparing them with previous partners. This provides a strong incentive to abstain from sex before marriage, to protect the emotional safety that spouses need to feel together in marriage. Every woman prefers to marry a man who has lived chastely. Similarly every man, in his heart of hearts, wants to marry a virgin, rather than someone who has been "test-driven" by scores of other men.

As one happily married woman described it on her internet posting: "I've only been with one guy; he was only with one girl -- and it wasn't until our wedding night. Maybe we were both bad in bed. But, you know, neither one of us had any clue, because we'd never been with anyone else. I've never seen that as an issue."

Singer/actress Rebecca St. James, who also participated in the Fox News roundtable, echoed the same sentiments: "Can I just say married sex (and I've never been with anyone other than my husband) is wonderful. It's so cherishing and beautiful, and I'm so glad I don't have any memories with anyone else, and I'm glad my husband doesn't have anybody to compare me to. We only have each other."

Dating and marriage are about commitment and sacrificial love for another person, not comparison shopping for the best deal, or test driving the latest vehicle. Sex is a unique gift by which we hand ourselves over to another within marriage, and cement the treasure of marital love in a permanent commitment to one another.

Father Tadeusz Pacholczyk, Ph.D. earned his doctorate in neuroscience from Yale and did post-doctoral work at Harvard. He is a priest of the diocese of Fall River, and serves as the Director of Education at The National Catholic Bioethics Center in Philadelphia. See www.ncbcenter.org.