Hardly orthogonal: better to exist in suffering or not exist is rather acutely the topic of interest to those contemplating suicide.
Conflating the two makes one argue ethics from a realm of infinite possibilities instead of focusing on reality, which doesn't really make for great moral choices. For instance, should people have as much unprotected sex as possible, without any regard to their or their offspring's well-being, just to give the most children the chance to exist?