[Avodah] what actually is the issur

[SBA]

From: "M Cohen" <>
..., what actually is the issur for a Jewish lady to sing in front 
of nJewish men (ie when l'fnei iver is not an issue)?  
>>

Which reminds me of a discussion recently, if there is any 
issur (and if so, what?) to own a brothel - where all the 
employees and customers are not mibnei bris?

This came up after someone claimed that the 'hetter' for a frum doctor
who has gone over to specialising in 'enhancing' the non-tzenius
parts of females' bodies, was, that he is osek bimelachto and 
thus spared from hirhurim.

So the question arose re using a similar 'hetter' to operate a brothel.