I think that in this case, the offense is far more egregious because the filmmakers have simply reused a title that people are somewhat familiar with, for no reason other than that it will seem somewhat familiar to people. Boring.
The movie is about a gay couple and their children. One day, the kids decide to find their genetic father, so they contact the sperm bank who puts them in touch with dad. Mom and mom are unsure about it until they meet him, and guess what? One of them likes him and the other one doesn't.
It's funny, too, that a movie about such an unconventional family could be told in such a conventional way. From the beginning, one could predict exactly what would happen in the movie. Who sleeps with who and who ends up being a jerk and who makes up in the end and where everyone winds up. It's all predictable and blah, blah, blah.
However, the actors, especially Julianne Moore and Mark Ruffalo make the movie not just bearable, but incredibly entertaining. Their time together on-screen is especially great, though a dinner scene late in the film with Ruffalo and Annette Bening singing Joni Mitchell is probably the film's shining moment. All in all, it's quite good.