Just from my observations, I don’t believe it has anything to do with ‘frowning on contraception” but instead, parents and children not discussing the issue. For many, the entire subject is ‘taboo’. When teenagers rebel, as they do, they gravitate towards what seems taboo (be it drinking, smoking, sex, etc), especially if their parents didn’t discuss with them consequences, etc.
I know that's what the Freudians used to love to say. But everyone knows the consequences. Religious people's kids rebel, as all teenagers do to some extent, but as a group (in my observation), their scale of rebellion is 10 on the scale of 100. The children of atheists living on Central Park West in NYC filling out the "100" end of the scale with drugs, sex changes, and suicides.