Three-parent baby: Is it ethical?

The UK was the first country to legalise mitochondrial donation in October 2015 (1). In 2016, the first three-parent baby was born in Mexico (2) and the US Food and Drug Administration declared that further research on mitochondrial donation is ethically permissible (3). It has now become an important issue, raising as it does, the spectre of "genetically modified designer babies".