Many advocates have said that, with the advent of contraception, gay and straight sex are just the same. (Actually a lot of orthodox Catholics make this claim too).
The Ruth Institute posted an October 2010 FRC study by Dr. Patrick Fagan and Dr. Sullins that analyzed nationally representative data from the National Survey of Family Growth to find out how religion and family structure affects the likelihood of unwanted pregnancies.
Here's the variation: Only 1 out of 3 women who grew up with both married parents and go to church weekly have an unintended pregnancy compared to almost 8 out of 10 women who grew up in other family structures and do not go to church at all.
Here's what strikes me the most though: even in the so-called "best case scenario" sex frequently leads to babies, whether or not the participants plan on it.
In trying to encourage young women who have sex to use contraception, we have considerably oversold the extent to which we have now changed the nature of sex between men and women. In the real world, I mean.