Why do a lot of feminists believe the differences between men and women are merely socially constructed?

This is something that's so easily debunked. If you take Estrogen or Testosterone it changes your appearance, personality, how you think.

Women think men don't open up cause it is shunned by society, in reality men just aren't as emotional.
Why do a lot of feminists believe the differences between men and women are merely socially constructed?
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