migoo, it’s not lo sasuru because we are not looking at the men to look at the men. It’s as if you would say that women can’t attend baseball games because of lo sasuru. Shuls would not be set up the way they are if it were really an issur d’oraisa. And by the way, a man singing can be ervah too (think Frank Sinatra, Elvis, and other crooners). I am not arguing with the halacha, just saying that it’s not always so simple and one must be careful. The “spirit of the halacha” is also a consideration.
Toi, that is exactly why I daven at a shul that lets women dance (on our own side, out of sight of the men, thank you very much). I could never stand around watching the men and twiddling my thumbs. Of course it would not happen the other way around, and of course men and women are different and have different attractions. My point is that we are less different than one might think, and furthermore that tznius applies to men as well. I think it is sad that we continue to pile chumra upon chumra on the women with regard to tznius while completely ignoring the men.