The big concern is that altering mtDNA eventually could lead to someone trying to make designer babies.
"The problem is that once we start saying we're going to allow inheritable genetic changes to make healthier children, then the next step is, we're going to allow these kinds of genetic engineering experiments to make children who are more intelligent or more athletic or have perfect pitch," Darnovsky says.
That's such a frustrating line of thought. It's not a slippery slope as soon as we start making heritable changes: a clear distinction remains between elective enhancements and preventing terrible diseases.
Now personally, I'm really hoping we do take biological evolution into our own hands once we have the technological capability; I'm all for some "intelligent design". But this is not that debate - with mtDNA it's a question of preventing a lot of unnecessary suffering, versus crossing a line (of heritability) that can apparently be conflated with the morally debatable one (of enhancement).