Full Idea
The main utilitarian objection to killing (that it results in the loss of future years of happiness) seems an equally powerful objection to deliberately not conceiving a happy child.
Gist of Idea
If killing is wrong because it destroys future happiness, not conceiving a happy child is also wrong
Source
Jonathan Glover (Causing Death and Saving Lives [1977], §4.4)
Book Reference
Glover,Jonathan: 'Causing Death and Saving Lives' [Penguin 1982], p.72
A Reaction
This makes perfect sense, unless you give intrinsic value to existing lives, but none at all to potential lives. Virtue ethics helps here, but genetic engineering is a nightmare for Aristotle.