I think that is is because a lot of people do a lot of bad things just to have sex. Such as rape etc. Sex is suppose to be between two people who are devoted to each other and really care for each other then it is a beautiful thing.
Not to sound too contradictory, but that's not just a product of this generation. People have been having sex without being in love sine the dawn of man. While I absolutely agree with the posts here excluding the last one, I also believe that sex is viewed as "dirty" by our society at the baser level as a form of population control. Man is a sexual creature, and more often than not we give into our carnal desires. But if we totally gave into our primordial desires, society as we know it would collapse. Overpopulation, homelessness, poverty, famine, and disease would all be on a rampant rise, more so than it already is. Cities would overcrowd, people would loose jobs and homes... Pretty scary stuff. So while I'm not saying I condone the way our government/religions/society perceives sex, you can certainly understand where their fears lie. I can't speak for anyone else, but I was brought up in Catholic schools, and as such I feel I was given a vary warped view of sexuality. I learned from a young age that if I was to have sex, I would (in varied forms): Be a sinner, go to hell, get a sexually transmitted disease, get pregnant, etc. Naturally, it did not take me long to figure out that these things didn't necessarily happen every single time I had sex out of wedlock. Since those days I have learned that in moderation, and with protection, sex is a sublimely beautiful expression of our most basest humanity.
Sex is considered dirty because long ago sex was only for the man to enjoy in the 40's and 50's women for the most part just laid there, and let man ,do there business as it was called. So when those women became mothers they didn't talk about or teach their daughters about sex, or the dirty little secret...but then finally the sexual revolution came about, and most women realize that sex wasn't dirt and should be enjoyed by both men and women, there are some frigid women still out there that hasn't come to terms with sex as being a good thing,
I don't necessarily think that most people consider it dirty. Maybe by the Amish standards...I don't know. I think a lot of people might think pornography and the such is what's dirty. But the act of sex between a husband & wife or boyfriend & girlfriend isn't really considered dirty. As far as parents and children...I still don't think that parents want to give their children the impression that sex is dirty, but rather that there is an appropriate time, age and mental point you should be at before you engage in it. And of course, make them aware of the consequences such as, disease, pregnancy, etc.
As far as religions...I agree with Ladylena. Some religions will make you believe that it is wrong if you are not married and should only happen for creation purposes.
Sex wasn't created 2 be dirty God created sex 4 when your married its supposed 2 be 4 passion but this generation has maid it where that's all we think about and that's what makes it dirty cause people are having sex with people that they truely aren't passionate 4..
Sex is only considered to be dirty by people who are immature and too ignorant to see it as a beautiful thing. Without sex, we wouldn't be here.
It could get dirty if you make it public or it is illegal like rape but you should still have abstinence until you are married