[ Psychology ] Open Question : Why society have such double standards abt bro-sis relation and they look male-female with different angles?

P.S. - I don't have any brother dating or have boyfriend yet, But I wonder - ---- Why in general society have such double standard that when a brother oppose sister's relationship with her boyfriend then he's called protective-caring brother while if a poor sister shows a bit of her displeasure of being ignored by her brother or being treated as crap by his girlfriend/wife then she's tagged as intruder-jealous-interfering and what not?

Source: http://answers.yahoo.com/question/index?qid=20110809035911AAqFbZV

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