@JustJohnny @DuckKingLoow @SuperLutheran @Zealist @professionalbigot69 @Bad_Banner 8 Then Judah said to Onan, "Go in to your brother's wife and perform the duty of a brother-in-law to her, and raise up offspring for your brother."

9 But Onan knew that the offspring would not be his. So whenever he went in to his brother's wife he would waste the semen on the ground, so as not to give offspring to his brother.

10 And what he did was wicked in the sight of the LORD, and he put him to death also.

Contextually it looks like the problem was that he refused his duty to his brother, tribe, and fathers command.
He wasn’t pulling out because he was using her for pleasure, he was pulling out because he didn’t want to provide a son to his brothers wife