Tradition.
As far as I know, FIL is the only male I'm related to that is not intact. My dad is intact (and as we were a very open family so I saw it, his is the prototype 'normal' as far as my own mental preconceptions are concerned), my brothers are intact, my husband is intact, uncles, grandfathers, etc, etc, etc. So I've always been able to laugh off the if-you-don't-do-it-then "horror stories" as none of them have ever had problems (believe me, I'd know, we know what kind of birth control everyone is using, who has what disorder, everything, seriously, it's not a very 'private' family).
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