I think the difference has to do with trying to do something about & in the present, as opposed to trying to do something to change the future. You do the gene manipulation & things don't turn out as you'd hoped, then what?
An interesting point. But to me, that seems to be more of a practical concern rather than a moral one.
Compared to other forms of permanent alteration that will affect the future - eye surgery, for example - what makes genetic engineering uniquely immoral?