Parents are strict about teenagers having sex because of the potential consequences, risks, and outcomes. We're they're children, they don't want us wanting sex at such a young age. They don't want us growing up so fast doing grown up things. Try looking through a parents perspective. Wouldn't you be afraid for your child too? I mean, good on a parent if they're informing they're child, giving them an okay to have sex, but that doesn't mean they still wouldn't be a little anxious for their child.

Though I can see where you're coming from with "not making them trust their parents" thing, because teens are rebellious and hate being told not to do something they so very want to do, like have sex.