Betty and Jim have no respect for themselves or for any one else. They practically engage in sex out of boredom. You can't even call it animal behavior..because with few exceptions animals only mate for reproduction.
The whole experience is of intense competition..Males of many species engage in competition..battle to earn the right to copulate.
Betty and Jim lack meaning in life and lack meaningful sex.
Dagney and Francisco...despite having sex sans bands of matrimony..have followed a classically romantic model.
They know each other intimately,spirit, mind and body. They are great friends and most importantly they respect themselves and each other. They have standards, they are capable of judging the good from the best. Neither will accept substandard performance from themselves.
They value one another unlike Betty/Jim who value no one.
Sex with Dagney/Francisco is a celebration , union of two equals. They share their life force as being a valuable thing.
Jim imitates life.. Dagney is alive.
I love your answer. It’s a keeper.
I’ll tackle the sex issue, too.
“I’d never want to belong to a club that would have me as a member.”
Jim doesn’t think much of himself, and knows that the only women who could possibly consent to be with him must feel the same way about themselves.
Use your own experience here. When someone amazing is interested in you, you feel amazing. I remember in high school, if it turned out the person that had a crush on you was kind of a loser, you kind of wondered if that was the best you could do.....? And what did that say about you if that particular person thought that they had a chance with you? Yeesh. (ooops, been there, done that!)
Dagny and Francisco are internally calibrated to their own wonderfulness (to the point of obnoxiousness, really) so they would never consider being attracted to anyone that wasn’t perfectly wonderful, as well.
Daney and Francisco make love with their minds... Jim and Betty have sex with their bodies.