Last year, Biggest Loser trainer Jillian Michaels got into some natalist hot water when, in an interview with Women's Health, she was quoted out of context when she said, "I'm going to adopt. I can't handle doing that to my body. Also, when you rescue something, it's like rescuing a part of yourself." As it turns out, Michaels has endometriosis and polycystic ovary syndrome (PCOS) — conditions that have already been mentioned here in the comments as a reason that some women choose not to have biological children.
In my opinion, the strangest persistent belief about childfree women is that we're selfish. From the jump, this is problematic as this logic negates the experiences of infertile women, women ambivalent about motherhood and parenting, and women who would—for any number of reasons and because of any combination of circumstances—perhaps like to be mothers but have opted out nonetheless. It's also a pretty big slap in the face to queer women, who may not face the same social pressures to procreate but may still be held to the same weirdo standard when they don't have children.