Obviously the pen is preferable. But in the U.S. impossible. There were 16 slave states in the U.S., 18 free states. Since there was absolutely no interest among the slave states in ending slavery by any means, compensated or otherwise, the chance of getting an amendment through the Congress was zero. In order to get it through Consitutional convention it would have taken 38 free states. Do the math, that's 64 total states. Lincoln could add, he knew that he could not end slavery. But he could try and halt the expansion. Which is what he advocated and which is what the South saw as threatening. So they rebelled. And they chose war to further their aims. Lincoln waged the war they forced upon him.
But fine, you back him up, I don't.
Facts back up Lincoln better than I can.