Almost no one will assert they think men and women are exactly the same.
So if everyone starts from the presumption that there is some, poorly defined, somewhat-conscious, never agreed upon, but certainly real, difference between men and women ... a bias in treatment would be the default condition, and would probably require conscious effort and/or policy to overcome.
Ironically, people usually assume that the unequal treatment benefits men over women, and completely dismiss the reverse possibility, even though there's no rational reason for this :)
It's well acknowledged that men are discriminated against in some contexts, but yes, there is no serious debate that the sexism in our society overwhelmingly targets women, and there's a reason that the movement for equality between sexes is called "feminism".
Except you're going to have a hard time pointing to any of the places where feminism is fighting against this well-acknowledged discrimination against men.
...And that's fine! Really, it's okay to say "this is the movement for women's equality meeting here in this room, if you're interested in men's issues you're going to have to go somewhere else." The NAACP doesn't spend all its time fighting against anti-Semitism, after all, and that doesn't make the NAACP bad in any way. I don't understand the weird compulsion to try and crowd everyone else out of the gender equality mindspace.