But the prominent playwright and gay activist Larry Kramer has seen fit to suggest otherwise, and it is causing no end of stink among the scholars, curators and amateur historians who consider it their business to safeguard the memory of the Father of the Nation.
Mr Kramer, who founded the radical Aids support group ACTUP and wrote the play The Normal Heart about the early years of the epidemic, claims to have seen a secret diary kept by Lincoln's lifelong friend Joshua Speed, in which the pair come off as rather more than bosom buddies.
"He often kisses me when I tease him, often to shut me up. He would grab me in his long arms and hug and hug," reads one of the few passages Mr Kramer has so far chosen to make public. "Yes, our Abe is like a schoolgirl," reads another.
Apparently, the two spent time wondering if other men had the same sort of relationship as they had. And - the topper, this - Mr Kramer suggests that Lincoln's assassin, John Wilkes Booth, may have killed the president to spurn his sexual advances following an introduction by Speed.
Since Mr Kramer first made his case at a public lecture at the University of Wisconsin a few months ago, Lincoln specialists have been asking the same question: where's the evidence? Mr Kramer has refused to show anyone the diary or give more than a flavour of it, saying he is working on an extended magazine piece about his discoveries as well as a book examining the issue of repressed homosexuality throughout US history.
That, naturally, has satisfied absolutely nobody, and already sceptics are insisting that no diary of this nature could possibly have survived undetected for so long. The building housing Joshua Speed's office, where Mr Kramer says the diary was discovered beneath the floorboards, burned down in 1855 and any concealed documents are likely to have been destroyed.
The real furore, however, began after the local paper in Lincoln's hometown of Springfield, Illinois, recently decided to splash Mr Kramer's theories across the front page. Readers became so infuriated at what they saw as an unsubstantiated slur on their local hero that the paper's editor was forced to apologise for daring to put the words "Lincoln" and "gay" in the same headline.
"Honest Abe must be spinning in his Oak Ridge grave wondering what he did to Springfield to make them shame him in this manner," one letter to the paper read.
The folks at the Lincoln Home National Historic Site take an equally dim view. "From our perspective, discussions such as these have always come and gone," said the superintendent, Norman Hellmers, voicing considerable distaste for the sensationalism in Mr Kramer's theory which he referred to simply as "that".
"That's just one of many things raised down the years, whether in positive, negative, or neutral ways."
Some of the historical record, it must be said, stands in Mr Kramer's favour. Lincoln became extremely close to Speed after he established himself in Springfield in 1838, and shared a bed with him when money was tight. Their published correspondence shows up considerable trepidation on the issue of marriage, and awkwardness about women in general. On the other hand, Lincoln had girlfriends, including one he proposed to, long before he settled down with Mary Todd. And although his political enemies spread rumours when he was running for president, they never suggested he was homosexual.
It is a debate where everyone has a stake above and beyond the historical truth about Abraham Lincoln. Mr Kramer makes no secret of the fact that he wants to reclaim as much of American history as possible for the gay cause. The establishment in Springfield has a certain, rather conservative civic pride to uphold.
Lincoln is such an icon that he has been an alluring figurehead for interest groups of all kinds. "People find it useful to exploit Mr Lincoln for their own purposes," Mr Hellmers observed. "They will do whatever it takes to make the connection." Including, it seems, tussling over his sexuality 134 years after it ceased to have any practical significance.