Let's assess that argument that religious teens who have sex will be less likely to use a condom because they have not been taught to act rationally with respect to sex.
The Add Health Study asked teens: 1) if they have ever had sex; and 2) if so, did they ever use a condom? A sample of 516 youths admitted to sexual intercourse. Here are the percentages who have used a condom by importance of religion to self:
Percent of those who've had sex who have used a condom
Very important 58.1
Fairly important 62.8
Fairly unimportant 64.6
The probability of condom use falls a little with greater religiosity, but none of the differences is statistically significant.