The prediction that human cloning will be available in 50 years raises issues, good, bad and downright ugly. Whether it is ethical will depend on whether the 'good' is sufficient to outweigh the potential 'bad' and 'ugly'. But good and bad in this context are not easy to define or measure. Even supposing there were good reasons for using human cloning, and that is a big if, it would need to be a pressing need to outweigh the potential for harm. Currently the risk of abnormalities is high.
It has been suggested that cloning might be used to replace a lost child with a copy. And it is here a myth takes hold: the idea that cloning produces an identical human being. This is the stuff of science fiction, not of biology. Cloning will not produce an identical, like for like human being. A cloned human will not develop and become identical to the person from whom this being has been cloned. If we wanted to clone a person rather than an organism, it is highly unlikely we could succeed. A person has a unique history and a unique development; their hopes, fears, loves and hates are as likely to be as different as any other two people.
But even biologically they will be different. They are likely, for example, to carry different risks of health and disease. Recent work on the developmental origins of health and disease indicate that much of the health risks we carry are environmentally determined during development in the womb and in early life. It is highly unlikely this could be replicated. A cloned human will be as unique as any other human. They are also likely to carry risks specific to being cloned.
But let us consider the idea of producing a replacement for a lost child. The psycho-social environment in which such a child develops would include the fulfilment or otherwise of the parents needs. The burden of needing to be like the 'lost child' will make it less likely to be successful. Better to be wanted as the person you are or will become than to always feel the need to be like someone else. The motives of such parents and their ability to adjust would be crucial. Perhaps they should not want to replace a 'lost child' but simply to have a child with his or her own personality. Psycho-social counselling would be better than a risky biological fix.
Much of human development occurs after birth. This is particularly true of brain development and function which are critically dependent on sensory input and social interaction. Environmental influences are a major feature in determining the function of our brains and our characteristics. In this sense alone we will each have a different trajectory, and this is one of the reasons why 'identical' twins are not what their name suggests, identical.