@tigerbasil
I 100% agree with you. I also come from a "non-conventional" family with one wonderful, wonderful parent. But I absolutely wanted to have a normal family with my two biological parents in a relationship when growing up. That was what all of my friends had. I was very conscious of being different, and not knowing one side of my family. You can't have a child with no father or mother, you are simply denying that one or both exists, he or she is still out there with half of the child's genetic material, as the child will be acutely aware from an early age (eg early primary school when everyone is making Mother's Day and Father's Day cards and talking about their parents - I don't doubt my "My Dad" story which was displayed on the wall with all of the others raised eyebrows among other parents).
I am very conventional in my outlook - I would never dream of deliberately having children on my own or other than in a stable relationship with the other biological parent, no doubt because of my own issues growing up. I find that my views on this are at odds with most of my friends, all of whom grew up in stable, conventional families. I do feel like it's easy for them to say, "all that matters is love".
Yes there are lots of bad family set-ups - but most people do not deliberately condemn a child to emotional burdens in this way. You wouldn't say eg "I have severe uncontrollable anger management issues, but I'm going to have a child anyway as there are lots of parents who beat their children."
I have to say the discussions on surrogacy and same-sex parents and anonymous donors frequently anger me, as it is so common for the discussion not to touch on the child at all, it is all about the adults.
As to the argument that it's better for someone to exist than not, that would justify so many things, like:
(1) "I'm a crack cocaine addict but I really want to get pregnant right now, should I go ahead even if I'll be taking crack cocaine throughout pregnancy?"
(2) "I have a deep desire to be pregnant and give birth but I don't want to raise a child or be traceable in any way - should I get pregnant, then have the baby and leave it on a doorstep?"
etc...