It's clear that having Lincoln curse in the film is historically inaccurate.
“The historical record is clear that Lincoln definitely did not tolerate
profanity around him,” Barton says. “There are records of him
confronting military generals if he heard about them cursing.
Furthermore, the F-word used by Bilbo was virtually nonexistent in that
day and it definitely would not have been used around Lincoln. If
Lincoln had heard it, it is certain that he would instantly have
delivered a severe rebuke.”
I think, however, that most people need to start realizing that when they go to see a movie today they're not getting 21st Century Americans becoming historical figures, but historical figures becoming 21st Century Americans.