Toi: I sort of agreed with you until your last sentence. One is the letter of the law while the other distorts the spirit of the law. There is really no “spirit of the law” concept in Judaism. We aren’t Doresh Ta’amah Dikrah. If Halachah tells us something is Muttar or Assur then we listen to that, regardless of whatever feeling someone has as to what the Torah thinks is right or wrong. I’ll give you a perfect example. A growing Baalas Tshuvah once asked me what Hashem wants, that she should fast and lay in bed all day on Yom Kippur or eat a bit and go to Shul? She said that since the point of fasting is only to help us focus on our Tefillos and the day, why should she fast?
I’m only talking M’ikar Hadin though. Granted, if a man sees that he is attracted to a woman sitting in a seat on a bus he should not sit next to her. It very quickly goes from Muttar Lechatchilah to Yeihareh V’al Ya’avor with no middle ground. A person has to have Seichel about it. I don’t think mandating men and women to sit apart is called Seichel. I do think that people realizing their own issues and avoiding them is called Seichel.