Not because it legitimizes non-partnered parenting. Because it's ungrammatical and INACCURATE! It was one thing when it was "Baby's mama" as it started, but to drop the possessive? *insert voice of Wallace Shawn* INCONCEIVABLE!
Also many of the children being discussed are NOT BABIES. You are not the baby mama of a 6 year old. You are the CHILD'S MOTHER!
We can't just start dropping possessives willy nilly. Where will it end? It won't. I am boycotting any publication that legitimizes the unforgivably ungrammatical nature of this phrase, and I request that y'all do the same.
What to call the other parent of a person's child?
Dame/Sire of his/her bastard offspring
Co-Parent to his/her child
*unintelligible grunting that cannot be recognized as speech*