News that President Obama's late mother, S. Ann Dunham, was posthumously baptized into the Latter-day Saints faith shouldn't be a surprise to anyone who's followed stories of this practice.
At one point Jewish organizations asked the LDS Church to stop the practice of baptizing Holocaust victims.
There was another story a few years ago that Adolf Hitler had been baptized.
Of course these people are all dead; they aren't dug up and immersed in a baptismal font. Someone stands in for them and is dunked in their stead. The idea took hold in the late 1800s when church president Wilford Woodruff was baptized for the signers of the Declaration of Independence after a "vision" in which the Founding Fathers came to him and asked for the baptism. In the modern church the practice goes on, but church rules require the people baptized are relatives of the living persons, not celebrities like Elvis, or world figures like Czar Nicholas...or Hitler...not unless a descendent of the person is a Mormon and puts the name in for baptism.
Like a lot of religious practices around the world that seem strange to outsiders, the LDS practice of baptism for the dead has raised more than a few eyebrows. The church always feels uncomfortable when asked to explain itself about unusual doctrines and inevitably some testiness will arise. Some who defend the practice of baptism by proxy might say, "Well, the person doesn't have to accept it, so what's the big deal?" I assume this means that when informed of this baptism, the baptized person from his place in the afterlife can choose to accept it or reject it. The discomfort of surviving family members knowing that some church is trying to turn their ancestors into Mormons isn't considered. The "what's the big deal?" attitude is usually a sign that the person questioned knows an answer based on his faith won't be acceptable to the questioner.
There were embarrassing incidents years ago surrounding what is euphemistically called baseball baptisms (baptisms under false pretenses). Mormon missionaries were given quotas and teenage boys were targeted for baptism. There's an interesting article about it here. As with the baptisms for the dead, current Mormons are reluctant to discuss, if not outright hostile with questions about the baseball baptism program.
Last year the LDS Church had a problem with negative publicity over polygamy. They were aggressive about distancing themselves from the FLDS group of polygamists who made the news by having their children taken into state custody. They have an ongoing problem with the HBO series, Big Love, about a man living with three wives.
I was raised in the LDS faith, but dropped out when I was 17. At the time I didn't know of any of these practices. I have polygamist ancestry but my parents told me polygamy no longer existed. I don't remember anyone mentioning baptism for the dead, and my active membership was concurrent with the baseball baptisms, but I never heard anything about them.
I'm sure there wasn't any malice attached to the baptism of President Obama's mother. It was probably just some zealous member who thought he was doing the woman a favor. I doubt any of Ann Dunham's descendents are LDS, and if told of the posthumous baptism Obama might be puzzled, but I don't know if he'd be offended. However, some people of other faiths are very offended by the practice and it rears its head every time a high profile incident like this occurs. The church should police its baptisms more carefully, but it's impossible to rein in members who go above and beyond the call of duty in trying to haul the unwilling into their idea of salvation.