It seems that there are some people posting who confuse Litvish with modern.
Completely incorrect. The litvish gedolim (such as the Moetzes in Europe, Rav Moshe, Rav Aharon, Rav Shneur, etc.) Pasken L’Halacha that an actual mechitza is not required at events, just separation, and that families should sit together at the Shabbos table even with other families (Famous story with Rav Shneur regarding that point). The Chassidish Gedolim (Ger, Satmer, etc.) held L’Halacha that men and women should be separated by mechitzos, not eat together on shabbos, etc.
The source of the Machlokes is how the Bais Hamikdash was set up during the Simchos Bais Hashoeiva.
The story goes that at the first Moetzes in Europe, there was no mechitza set up (the women were on a balcony). They were all ready to start, when the (IIRC) Gerrer Rebbe threatened to walk out because the lack of a mechitza was against his shitta. L’maan Hashalom, they gave in, and ever since, the Agaudah has had mechitzos.