Islam does not prevent singing and dancing but it forbids anything that is provocative or stimulates peoples desires whether it be among men or women. Men and women dancing together is not allowed except when a wife dances in front of her husband and ofcourse mujras or dances of the kind mentioned above are not allowed in Islam. I am no scholar but I don’t think such ‘immoral’ acts are punishable by death. Dancing that is seen in weddings is not meant to be sexually provocative to anyone, so perhaps it is allowed, but again I am no scholar. There are many muslims who drink (which is unlawful) but does it mean we go and kill them!!
The Prophet pbuh himself used to encourage his people to sing and rejoice on special occasions, and the Quran encourages us to beautify our voices when reciting it.
And as I understand it one of the imams Imam Shafiee was fairly relaxed on the matter of dancing. As per one Hadeeth, the Prophet Pbuh saw a group of Abyssinians (people of Ethiopia who were famous for singing and dancing) in the Mosque and did not stop them. Therefore this will be classed as tacit approval from the Propht Pbuh. It is also stated that the Prophet allowed his wife Hazrar Ayesha 
to see the dance of the Abyssinians.