Putting on my amateur psychologist hat, might it be a defense mechanism? After all, no man who has been sexually free can know how many children he has fathered.
But I know that there are men out there who can't even make the mental connection between intercourse and fatherhood. It strikes them as a non sequitur, a total disconnect. They don't even spend one nanosecond thinking about contraception. Huh? Whatever. "That's her problem, not mine."
There are women more or less like that too, of course. If they get "unexpectedly" pregnant --- after having 300 million live sperm inserted into their genital tract --- they are shocked, then angry. "It's so unfair!"
Feminist novelist Marge Piercy said it's absurd that you can "catch" a baby as easily as catching a cold. Women were created with this design flaw, y'see. Achieving pregnancy ought to have required a far more elaborate and steadily intentional process, unconnected with the vagaries of mood and passion.
I haven't much to do with people like that.