Apparently the "hot" new thing when it comes to raising kids is something called co-parenting. It used to refer to divorced or separated parents trying to amicably work together to ensure that their child was raised well. (As a a kid from a divorced family, I know a lot about this.) Now, using sites like co-parents.net, people are coming together to have children outside of any formalized relationship or commitment.
It may sound like a convenient solution to some, but, as someone who grew up in a household touched by divorce, I can't in my wildest imagination understand why parents would willingly wish this upon their children. If they want a pet, go get a dog or a cat. A child is not a pet, and a child deserves two parents devoted to each other in a loving, committed, and formalized relationship.
In essence, this practice is using the tragedy of divorce and of children being shuttled between parents like luggage as its operational model. Talk about self-centered. How about considering for a moment the best interest of the child instead of yourself. It will be interesting (and profoundly sad) t o see how dysfunctional and cynical the children of these imaginary relationships become as young adults.