I got rhythm

As far as I can tell, no one's reading this. Fine. Then apparently my question will go unanswered.

I need someone, preferably a priest, to explain catholic birth control to me. What makes it acceptable by church standards?

While going through marriage training, we discussed many things: kids, money, church, work and sex. We also discussed kids and sex together. Fortunately, these discussions were led by married couples, because I wouldn't be able to take a priest seriously on the subject of sex. In theory, he knows nothing about it. If he does, he's a liar at best. So we discussed what is commonly known as the "rhythm method", though I've been assured it's far more sophisticated than that.

The theory goes this way:

• Women are not fertile at all stages of their menstrual cycle.
• Sperm live only for a few days.
• It's safe to have sex with a woman (preferably your wife, for a number of reasons, not the least of which is the horrifyingly poor success rate of this method of contraception) during these days of infertility (some of which, according to the OT, she is unclean) if you are trying to avoid contraception.
• The sperm will die before the egg is released.
  
• The methods to determine the safe days for sex include counting days, measurements of things like temperature, the dilation of the cervix, and the consistency of the mucous within (presumably not the taste, because that's a sin, I've been told).
• This is approved by a bunch of men who aren't supposed to be having sex with anyone.
• It's also supposed to be good for trying to have a baby, because then you can figure out the most fertile days and shoot for them (pardon the pun). This must be because just having a lot of sex all the time seems too much like fun for the church.

So, assuming this works, answer me this, smart guy:

What makes this Pope-approved?

Assuming that I, using the rhythm method, ejaculate inside my wife, knowing that there's no chance of her getting knocked up, how is this different from a number of other ways to ejaculate knowing there's no chance of conception? If my wife gives me head, and I come in her mouth, isn't that a sin because she can't get pregnant? During anal sex? Using a condom? When she's on the pill? Just jerking off, even if my wife is there or if I think about my wife? Aren't all these things sins because I'm experiencing orgasm and my seed is spilled, to speak biblically?

Wasting semen, I'm told, is bad. It's baby-making batter, and a gift from god. So, ejaculating in the vagina is the way to go. But if we don't want kids, we have to time it so she can't get pregnant. I'm belabouring a point here, but I want to be perfectly clear.

I'm guessing that the chief selling feature of the rhythm method for the RCC is its unreliability. Married couples are supposed to have kids. Preferably catholic ones. But any other kind is good too (except atheist ones, according to the pope). That's why gay couples can't get married (sorry, guys). We won't talk about barren folks or senior citizens because we're not allowed to discriminate against them (although, barrenness could be considered an imperfection, especially to a god so hell bent on knocking women up, and then you can't go to church anyway; it's somewhere in Leviticus, I think). Contraception is not cool. Not condoms, not the pill, and jerking off is a sin, too.

Maybe if priests could have sex, they wouldn't be so fixated on it. Or on kids.