That is because you were indoctrinated to feel that way, likely by your parents, or if not, by society as a whole, which has always treated sex as something dirty or at least naughty. I still would be uncomfortable today even if my mother wanted to talk about sex with me or she wanted to talk about how her sex life with dad was, but with 10 pregnancies, 2 miscarriages, and 8 delivered live children, they must have done it somewhere sometime, and we had a relatively small house where we were not in our parent's bedroom, but we could certainly have heard them if they had been making any verbal comments relating to their lovemaking.<quoted text>
"In some cultures, parents have sex in front of their children. It is seen as a natural part of life"
In what crazy way is it natural for a child to watch their patents have sex?!
In American culture, and in all civilized societies, nudity is a private thing and an adult thing. There's no justifiable reason that a child should see their parents naked. I remember getting creeped out just HEARING my parents screwing in the next room. I was never afraid of nudity or sex, but when it comes to ones parents, it's a whole nother ball game.
Some things should stay sacred. Parents having sex away from their kids eyes & ears needs to be one of them.
I never once thought my parents were in the act of having sex right up to living with them for a couple months after I had been married for part of a year, and had moved back to the farm from university, but as yet did not have a home of my own.
Whether any of my siblings ever caught them in the act, I don't know, because none ever mentioned it to me.