Why were Krishna's parents, Devaki and Vasudeva  subject to such cruelty and punishment?  Why could the supreme being not have been born in a palace with a multitude of attendants to care for his well being.  Why did he have to be preceded by murder and death and had to be smuggled out in darkness, floated on water and be brought up by foster parents? Why did he not have a pleasant childhood? Why was he visited constantly by demons in different forms?

Krishna's birth and life illustrates that the birth and development of the human intellect is fraught with dangers, happens in a hostile environment and is subject to challenges right through its worldly existence. 

Life takes birth in the womb of women, which is the first container, the prison.  The baby struggles through the passage of the uterus, and gets delivered into this world. The real parent (Easwara) entrusts the baby to its worldly foster parents.  The child is subject to illness (the demons), develops immunities to fight them, overcomes its own ignorance of the ways of this world by encountering hostile and friendly people and so on........

Krishna's worldly appearance is meant to illustrate the very fragile and difficult environment in which life is created, sustained and developed.