People who don't have children are selfish...wait, what?

I'm at the time in my life when people ask "When are you having kids?". I shrug, say "I dunno, maybe never." Usually I get a disinterested "Okay." but more than once I've gotten "That's selfish". I stop, make sure I'm awake, and then search for my Crazy-to-English dictionary.

This really got me thinking. Not sharing your toys when you were 6? Selfish. Eating a big bag of candy and not letting anyone else have any? Also kinda selfish. Not currently keen on welcoming perfect strangers to board in my uterus for 9 months and then being lawfully, psychologically and physically driven to care for them for the rest of their existence? Apparently that's right up there with stealing people's cabs and pushing the "close door" button when someone is running for the elevator.

I've really thought on this and the following is me trying to make sense of it all:

There won't be anyone to refill blood banks...

There's a waiting room for earth and I'm holding up the line...

I carry rare genetic code that the human race desperately needs to ensure the survival of our species...

Minivan salesmen will go hungry ...

I'm still at a loss.