Genetics don't matter
People at work were recently saying that they'd never donate sperm or eggs because there'd be a child with their genetics out there that they didn't know about. Upon my inquiring why that would matter, they essentially proclaimed that anyone who doesn't consider such a thing important is a bad parent. 'You came from my seed, but it doesn't matter.' == Bad parent.
This has some obvious logical consequences: I know of families where one child was born to them and one was adopted. They do not favour one child over the other. Therefore, ceteris paribus, they do not care that Child A has their genetics, and therefore these people are bad parents.
My conclusion is slightly different: I've observed that these people are good parents, and therefore, the people I work with are wrong (because, like most people, they've bought into the whole 'bloodline' idiocy we were supposed to have abandoned when we left the hereditary monarchy in favour of meritocracy). Genetics are a medical matter. It's the social aspects (IE, who raised you) that should matter to us socially.