An other reason might be that almost all animals seek to control their peers' access to mates.
Humans have developed elaborate bullshit to achieve basically that. Monogamy, possession, shame.
Humans have developed elaborate bullshit to achieve basically that. Monogamy, possession, shame.
Throughout our history, it's also mostly practiced out of necessity/pressure by the underclasses/commoners* of human society, not the rulers/leaders/wealthy.
* (not counting prostitution)
"Acting selfishly" is also a common victim-blame.
Not sharing your lunch money with povert bullies, or loving someone you love instead of whomever other people want you to love.
I’m ashamed.