It isn't, as monogamy is the societal standard, so by that guy's logic wouldn't they have defective personalities because they sleep with several people in a night? Also you ignored the fact that most of the people being shamed for being a virgin are young men and teenagers, do you expect boys to lose their virginity by 16 or something? So because, say an 18 year old is a virgin, he has a 'defective' personality.

EDIT: I am ok with polygamy BTW, if you're into that than go for it. The first statement is for hypothetical purposes.