This embodies the reason why Singer's philosophy ultimately breaks down and reveals itself, essentially, as madness. He invests the right to life of another person in the vague, arbitrary, and ever-changeable notion of the "happiness" of others, or another. There are so many flaws in this argument they almost cannot be listed in a relatively short space (e.g., what happens if a profoundly disable infant is born to parents who love it beyond measure? Are the parents "wrong" to love a disabled child? If not, how does it make the child any different if the parents did not love? What happens if one parent loves the child and the other doesn't? Which one has "priority", and what moral import to they have to claim such priority?).
This is why the culture of death either collapses of its own immorality, or results in measureless destruction and rivers of blood. In either case, it is incumbent on those of us to value human life and the dignity of the individual to oppose it with all our will.
Apparently, they are. (viz.Trig Palin)
It makes sense, because such loving parents shame the baby killers by their very existence. They need to watch their "six" accordingly.