Jojostar...UANBU...you're right, mothers like this don't deserve to be called mothers (no I'm not a girlfriend/second wife, I'm my husbands first wife, we share 1 dc and have another on the way...I am however, a child of divorce), in the same way that fathers who intentionally hurt their kids, or don't see their kids for 'no good reason' don't deserve to be called fathers.
Sadly both scenarios happen, and neither is forgivable.
Any selfish choice that a parent actively makes and thus hurts their child is completely unforgivable...parents are parents no matter mum or dad, and each has something different to offer...the ideal situation is that a kid has both parents, regardless of together or apart. Divorce is the end of a marriage, not parenthood...why do so many people miss this because of their own hurt.
I also don't think you are being unreasonable to have a rant here, why don't you have the right?
Can everyone stop for a minute and pat you on the back for obviously caring so much about your dsd's, that seems to be whats fueling your anger. Surely they are lucky girls to have a step mum who loves them too.
Yes I'd be hurt to see someone else 'mothering' my child, yes it would rip me appart...but I'd rather have him be loved than unwanted or resented...
As for two sides to every story...yes there are...and i'm sure that both sides have valid points(or at least believe they do)...but your original post wasn't about your story...it was about selfish mums who put their own games first...UANBU