[Infographic] The 30 Articles of the United Nations Universal Declaration of Human Rights
Another way to respond would be "Because they are." Because a lot of times characters will just create themselves and things like their race, sexuality, and gender just come naturally when writing them rather than being conscious decisions.
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Unless I engage in this conversation on emotional labor and actively change the roles we inhabit, our children will do the same. They are already following in our footsteps; we are leading them toward the same imbalance. http://fuckyeahwomenprotesting.tumblr.com/post/170175581725/when-i-brush-my-daughters-hair-and-elaborately
The 'ending' gender roles I don't like, because most kids and adults fit well in their gender roles and we can mske room for the outliers. But if you wont be happy untill gender roles are ended you will never be happy.