Irshad Manji is a Muslim journalist who wrote The Trouble with Islam Today: A Muslim's Call for Reform in Her Faith, about what Islam needs today, and why historically the Islamic world shut down its own tradition of intellectual inquiry about a millennium ago. A good book, and she's lucky to have survived its publication, being a lesbian Muslim.
Manji thinks Lincoln's understanding of duty is similar to Che Guevara's understanding of duty. She posts a poster of Lincoln with a communist star on a Che beret, all in red and black, like Obama's notorious poster during his first presidential campaign. No one objected to that poster, least of all Obama, and it undoubtedly gained votes for him.
The web has a solid tradition of people attributing uplifting or inspirational B.S. to whomever they like: the Dalai Lama supposedly said let cooking and lovemaking be unconfined, or something like that. People can't quote Jesus because we can look up quotes in the Bible, but they claim to know what He really thought about all sorts of pet causes. And Lincoln's sense of duty is somehow related to the murderous Che Guevara's. Perhaps Manji thinks anyone who pursues a goal through war, such as the war against slavery, is equivalent to every other person who uses violence. But the quotation has to do with the internal definition of duty, not with any external standards of right and wrong, which would take some explaining in this case. More explaining than can be conveyed in a poster designed to appeal to the reptilian brain.