Because… inert matter doesn’t make decisions…

Why is that good?

As long as you accept the premise that some people are happy and some people are unhappy, I don’t think measuring it for precision matters.

The claim is that people who experience unhappiness shouldn’t exist. Why would I accept a precisionless “unhappy” on these terms?

They wouldn’t be a child if they were never born to begin with.

They would still exist as something. Children don’t appear ex nihilio.

Your argument isn’t for non-existence. It is for non-sentience.