Permitting sinning to reduce it?

 Igros Moshe (O.C. 4:35) Concerning the issue of mixed dancing of men and women, it is clearly prohibited even if the woman are not Nida and surely is prohibited if they are Nida And they don’t refrain from dancing with married women.  It is not relevant to permit mixed dancing  with the claim that if you don’t permit it in the social hall they will go to the regular dance halls where they will be dancing with non-Jews.