Opposing condoms leads to a higher (STD) infection rate, teen pregnancies and it leads to humanity breeding out of control, the Catholic church is on record as opposing condoms.
As for the church being a teacher of sexual morality that is probably an even more inflammatory subject than this one already is.
Non-monogamous sex leads to a higher STD infection rate, too, and many atheists are on record supporting non-monogamous sex. If people were to fully adhere to Catholic doctrine, there would be even less risk of infection than if people were to fully adhere to the doctrine of using condoms but otherwise leaving their sexual behavior unchanged.
Newsflash:
"Almost all Americans have sex before marrying, according to premarital sex research that shows such behavior is the norm in the U.S. and has been for the past 50 years.
The new study shows that by age 20, 75% of Americans have had premarital sex. That number rises to 95% by age 44."
It's just that the doctrine isn't working, and it never has. Teaching people about condoms doesn't increase non-monogamous sex ratio's (those are high already), but it does increase condom usage. The guilt and exceptionally "sex-negative" culture that's been fostered in Western Culture, a large part due to Christianity, has caused us tremendous problems through sheer ignorance of human sexuality.
Unfortunately, it's often the women who are at the most at risk, even those in monogamous relationships (women are at a much higher risk of AIDS infection) as it's statistically the male who cheats and in many societies the ability to divorce is limited. This doesn't even touch on the power birth control and condom usage has given women in fully monogamous relationships to properly and effectively plan their pregnancies.
"Almost all Americans have sex before marrying, according to premarital sex research that shows such behavior is the norm in the U.S. and has been for the past 50 years."
I do not think the Catholic Church is unaware of this information nor does it dispute its veracity. I don't think you really believe that the Catholic Church is "sex negative," either. They strongly favor the association of sex with procreation, which is different than being against sex altogether. It is a minority viewpoint, but aren't minority viewpoints valuable and worth examining to see if society has gone too far in the opposite direction?
I also find it odd you see Western Culture as "sex negative." I would be surprised if you could name more than a couple popular Western TV shows or movies that endorse anything like the Catholic viewpoint on sex. Or did you mean something else by "sex negative?"
"Sex-Negative" is a term sociologist/anthropologists often use to describe different societies. I picked the term up from reading some of Helen Fisher's talks/papers about sex and romantic love (http://www.ted.com/index.php/speakers/helen_fisher.html).
"Sex negativity" is more about a lack of tolerance of different forms and viewpoints of sexuality.
I don't think that upon reading the Catechism or looking at a history of the Catholic Church and it's view on sex/sexuality you come away with a very comfortable view of the actual sex act. Part of this may be due to the fact that those that wrote the doctrine were suppose to be chaste. It's interesting reading how the Catholic Church changed it's early viewpoint from allowing priests to marry early on, to outlawing it (in all but a few loopholes, such as getting the "calling" after you are married).
Most of the doctrine seems to view sex as some unfortunate necessity for procreation, not something to be celebrated by itself. It's never been that comfortable with sex for pleasure. This is in stark contrast to let's say the Greek/Roman societies before the rise of Christianity.
However, I feel like the word itself is partly biased because it assumes that a "sex-negative" viewpoint is bad and a "sex-positive" viewpoint is good (similar to the atheists movement to call atheism "brights"... which makes it seem like everyone else is dims) instead of using more neutral definitions.
On the other hand, high levels of pre/extra-marital sex also correlate strongly with higher levels of STD infection. The Catholic church is pretty strongly against that too.
The problem is that in our society, it's unavoidable that people engage in pre/extra marietal sex. This is why abstinence based sex education lead to higher teen pregnancy (since they still have sex just without condom) and why one should just be pragmatic and condone the use of condoms...
As for the church being a teacher of sexual morality that is probably an even more inflammatory subject than this one already is.