In the old days, you kept romantic relationships casual and light by not having sex. Today, the opposite is true: declaring your abstinence before a woman makes her think you're moving waaaay too fast. How did that happen?
When sex became ripped from its original home (nestled among marriage and family) and treated like just another dating activity, it completely lost its status (for some people) as the single most profound thing that two people can share with each other on this earth and in this life. The underlying secular assumption is that sex belongs to the same category of human activities as eating, sleeping, and excreting. This contributes not only to the image of celibates as freaks but also lends credence to the prejudice that we're chomping at the bit to fulfill "biological imperatives".
Tell a woman you're "waiting" for marriage, and she assumes you're waiting impatiently. Cue decades of comittment anxieties and stereotypes of religious people, and you've already been written off as four walls short of a YFZ cultist and a warden of the domestic prison.
All of this leads to another irony, namely, that premarital sex has become the litmus test to ensure that someone isn't too comitted, i.e., that they're just as terrified of permanence as you are, and that they buy into the same cultural trivialization of sex as you do. So now sex has come to mean virtually the opposite of its original, natural message. No longer, "I give myself to you wholly and without reservations," wordlessly pulsing in and through the sexual rythm. Now: "I am helpless to resist you, but I give only what I must, and I withold everything that might lead to an inconvenience, or to something [shudder] permanent." Zero public unity, technologically frustrated fertility, a single, isolated act without reprocussions, differing from picking each other's noses only in the degree of endorphins released.
In a society where people will abandon their bodies to each other before they exchange names, it is lost on most women I've encountered that I believe in caution and patience when it comes to life's big decisions. I'm the last person who would hastily wed for the purpose of fulfilling "biological imperatives." I'm as much a comittment-o-phobe as anyone. But I refuse to despair of the unique happiness accessible only to long-wed, faithfully married couples, and to exchange that promise for a cheap and temporary substitute, robbing a potential future wife the status of my one and only.