Once again people are trying to make claims about some one who cannot confirm or deny the assertions because they are dead. Mansfield's "Abraham Lincoln's Atheist Period" is just the most recent example of living assholes trying to use the dead like they are some type of puppet. Personally, I don't have a problem with bring up someone's religious beliefs or lack of beliefs if it is relevant in a given discussion. I do have a major problem when a particular belief or trait of the deceased is either brought up for no good reason or is used for a personal agenda. It especially pisses me off when the trait or belief in question is exaggerated misrepresented, or an outright fabrication.
There may be some reason to believe that Lincoln went through a period where he became anti-religious but that does not mean he was an atheist. Mansfield references a few sources that claim he was hostile to religion. If you look at the details it would be more accurate to say he was opposed to a specific brand of Christianity not religion in general. It is also notable that he is described as hating or being angry with God (or rather a Biblical version of the God concept). If you are not a completely ignorant fool that should have caused you to rethink the use of the term "atheist." You can't get angry or hate an entity you do not believe exists in the first place. You can get angry at people around you for how they use the concept but that is not even close to being the same thing.
If Lincoln had been an atheist I would have no problem adding him to the list of positive role models related to non-belief. But he was not an atheist. So why does Mansfield want to make him out to have been one? Does he have an agenda? I don't honestly know. I can think of a few possible reasons others might want to do so. The article makes it clear that it was a passing phase in Lincoln's life. perhaps this is another attempt at smearing atheists. Somehow our thinking is immature or lacks any real thought. This is often what is implied when people talk about going through a phase. It could just be an interesting idea that caught his attention. I'm not sure. What I do know is that the piece exemplifies a variety of myths/stereotypes about atheism (we can't hate God, anti-religious sentiment is not synonymous with atheism...) and lack of understanding how historical research should be conducted. It is also galling since theist tend to be the loudest when calling for respecting the dead and yet they are usually the first to pull this type of propaganda-like bullshit.