Why do parents make it out to be shameful or down right dangerous to have safe sex?

My parents threaten to kill me and my SO over it and it's driving me mad. My sister skipped school to have sex, they were pissed but never once did they threaten to kill her. Me and my SO abstained for a while before we did even the smallest sexual acts.

They have me to the point that the idea of buying say condoms is terrifying.

Like what the hell? Does anyone else deal with that?