Lincoln's "compassion" is irrelevant, inasmuch as he was assassinated five days after Appomattox. The new U.S. president, Andrew Johnson, was a personal enemy of Davis since their days together in the Senate. Nor did Johnson share any of Lincoln's "compassion" toward the South.
The Johnson administration very much wanted to prosecute Davis for treason. It hired respected jurist Francis Lieber of Massachusetts to prepare the case against him (and, for good measure, to see if he could link Davis to the Lincoln murder). Lieber spent months poring over Confederate documents and could find absolutely zero evidence connecting Davis to Lincoln's assassination. So then the administration fell back on the charge of treason, and was advised by Lieber, "Davis will not be found guilty and we shall stand there completely beaten." (Foote, The Civil War, Vol. 3). Davis was released from Fortress Monroe after one year in solitary confinement.
The unconstitutionality of the doctrine of secession was not, in the mid-19th century, a cut-and-dried notion. In fact, when Mississippi seceded from the Union on Jan. 9, 1861, then-U.S. Senator Jefferson Davis did not immediately return to his home state, as did his other Southern colleagues. He stayed in D.C. for almost two weeks, hoping to be arrested for treason, thereby putting the constitutionality of secession in front of the courts...and possibly averting the war. The arrest never came. While Davis was incarcerated at Ft. Monroe, he spent much of his time preparing his legal defense, which of course would be a constitutional defense of secession. He never got the opportunity to use it.
Except for a backhanded slap at secession by a Reconstruction-era SCOTUS (1869) in an obscure bond case (Texas v White), the constitutionality of secession has never been specifically litigated. Until such time as it has, any reference to Lee, Davis, or any other Confederate as "traitors" is merely personal opinion without judicial concurrence. Surely you can understand how some people might find that offensive.
What would the charge have been? Loitering in DC may have been a misdemeanor, but just coming from a state where some had decided to secede wasn't. There would have had to have been some specific act on Davis's part, so I'm pretty sure he was safe, so far as the law went. He left DC well before he was chosen as POTCSA.
When prosecution for treason was considered after the war, there were all kinds of legal technicalities advanced as reasons not to have a trial. Most of them weren't very convincing. There was no trial because of the political awkwardness. It would have kept the country divided and a jury's verdict couldn't have been reliably predicted.
Until such time as it has, any reference to Lee, Davis, or any other Confederate as "traitors" is merely personal opinion without judicial concurrence. Surely you can understand how some people might find that offensive.
Ditto for Benedict Arnold, I believe. And even Alger Hiss wasn't convicted of treason.
But online, when has something being considered "offensive" put it off-limits?
What I find offensive is that these two launched a war to preserve an economic system based on the use of slave labor. As to the questions I asked you: If the South had won would they have ended slavery? And would they have been gracious to the North in it’s defeat. And finally why do you continue to defend these traitors, that’s what they were. As to Davis, that moron was one of the most prominent reasons the South lost the war.