The issue of "niceness" is separate from alignment. Someone can be a Lawful Evil type and be completely affable...to your face. In contrast, someone can be a genuinely good character and be pretty gruff. Jaheira (though she's technically True Neutral) is a good example.

I'm not sure I agree that the female characters need to be "nice." But Larian seems to have tied niceness to approval, and right now the female companions tend to be pretty cold/mean to you if you go around doing heroic things. This is disappointing, because I feel like as a good character I'm locked out of the female romance options (or even just a close friendship) due to not wanting to be an asshole to everyone.