To me, the solemnity of the actual wedding ceremony and the joyousness of the recption (which is a party, after all) are too entirely different things! The reception is supposed to be fun, so I see nothing wrong with chicken dances, silliness, etc. Most receptions feature alcohol in some form and alcohol is not associated with people acting serious and solemn (in my mind).
I wouldn't have a cake smash at my wedding but if it is done with a sense of fun by both members of the happy couple, I would laugh along with them.