Some people see never-existed people as moral agents, and claim that we can talk about their preferences. Generally this means their personal preference in existing versus non-existing. Formulations such "it is better for someone to have existed than not" reflect this way of thinking.
But if the preferences of never-existed are relevant, then their non-personal perferences are also relevant. Do they perfer a blue world or a pink one? Would they want us to change our political systems? Would they want us to not bring into existence some never-existent people they don't like?
It seems that those who are advocating bringing never-existent people into being in order to satisfy those people's preferences should be focusing their attention on their non-personal preferences instead. After all, we can only bring into being so many trillions of trillions of trillions; but there is no theoretical limit to the number of never-existent people whose non-personal preferences we can satisfy. Just get some reasonable measure across the preferences of never-existent people, and see if there's anything that sticks out from the mass.
I'm sympathetic to this line of thought, but setting the number to zero creates unnecessary problems. I think it would make more sense to set the utility of a dead person to be whatever the total amount of utility they experienced over their lifetime was. This has the same result of removing the incentive to kill unhappy people, since (for instance) people who died in their 20s would normally have much lower utility than people who lived to be 80. And it would remove certain counterintuitive results that zeroing produces, such as having someone who was tortured to death end up making the same contribution to the average as someone who died from excessive sex.