Why are girls more valuable than boys

DO YOU NOTICE THIS TOO? In general let's say a couple has a son and a daughter.
When the daughter is interested in boys, it's time to freak out. If she has sex, she's immediately deemed less in one way or another. She's not allowed to hang out with boys even if they're friends, barely allowed to go out. 
But with the son, "boys will be boys" and he can pretty much do what he wants. He doesn't get punished for having sex or deemed less of something because he did. 
Boys are pretty much, less valuable than girls. (I don't think that, that's just what it seems like) 

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