We all know that a shul must have a mechitza for davening. The source is a gemara in Succah [51b-52a. Some poskim learn from this gemara halacha li-myse that ALL public gatherings must be separate because that is what the gemara is talking about]. We will learn that gemara now and derive a great lesson for life.
Our Rabbis have taught, Originally the women used to sit within [the Court of the Women] while
the men were without, but as this caused levity, it was instituted that the women should sit without
and the men within. As this, however, still led to levity, it was instituted that the women should sit
above and the men below. But how could they do so? Is it not written, All this [do I give you] in writing as the Lord has made me wise by His hand upon me?
Rav answered, They found a Scriptural verse and expounded it: And the land shall mourn, every family apart; the family of the house of David apart, and their wives apart. Is it not, they said, an a fortiori [kal va-chomer] argument? If in the future when they will be engaged in mourning and the Evil Inclination will have no power over them, the Torah nevertheless says, men separately and women separately, how much more so now when they are engaged in rejoicing and the Evil Inclination has sway over them.
What is the cause of the mourning [mentioned in the last cited verse]?
R. Dosa and the Rabbis differ on the point. One explained, The cause is the slaying of Messiah the son of Joseph, and the other explained, The cause is the slaying of the Evil Inclination.
This is truly a wonder. At the end of days there will be no more yetzer hara [according to one opinion] and yet it will still be necessary to separate the men and the women with a mechitza. Why??? If there is no yetzer hara what can go wrong?!
Rav Yisrael Salanter: From here we see the power of HABIT. People are so used to being sinful that even when the impetus for the evil [the yetzer hara] is absent, they will continue to sin!! So maybe those who have so much time and energy to fight for women's appearance at public forums, should use some of that excess time and energy fighting for higher standards of Kedusha.
Of course the power of good is much greater. If one is on the habit of doing good then it will certainly carry over to instances even when one's yetzer tov is not activated. That is why is is worthwhile to adopt good habits:-).
