Is "sex" a cuss word?

Just a few minutes ago at around 7:40pm, my (21m) brother (9m) came downstairs after finding out that my bedroom door was open. The show, "Family Guy," was on. He asked me that when I leave the bedroom, I should close the door because the show is "too inappropriate."

I believed him, acknowledging and accepting the fact that FG was inappropriate. However, I asked him, "Didn't you say a few months ago that your parents let you watch that show sometimes?" He responded, "Um, that was The Simpsons." He added, "There's less S-E-X and other inappropriate things." I swear, he spelled out the word, which to me is exactly the same as saying it.

My brother also added regarding The Simpsons, because of "sensitive people," that show has actually become more appropriate and kid-friendly. I've watched both the old seasons and new seasons and they're absolutely no more appropriate than Futurama or Bob's Burgers, which everyone knows are adult shows.

But my stigma is where the word "sex" is at, and sexual content is the only specific thing my brother mentioned, not profanity or violence.