Wrong. Murderers and slavers can be stopped. (However, you have to be pragmatic.) The Constitution only protected the south while the south was in the union. After the south seceded, God help them.
Was it not the position of Lincoln that the South could not leave the Union, and therefore all those states remained part of the Union throughout the entire war?
Was his authority to send troops based on the idea he was stopping a rebellion or an insurrection?
Lincoln never recognized the Confederacy as an independent nation, his every legal claim was that they remained part of the Union, and if this was his stance, than the people of those states retained all the protections of the US Constitution. Or should have, if he was consistent, but it is clear that he himself didn't even believe his own lie on this point.
As I have stated numerous times, so far as Lincoln was concerned, the South existed in a perpetual state of quantum superposition, being both "in" the Union and "out" of the Union at the same time, depending upon what power Lincoln wished to utilize, or what legal argument he wished to put forth to justify what he was doing.
He played it both ways. When it suited him to regard them as "out", they were out. When it suited him to regard them as "in" they were in.
They were whatever he wanted them to be at any given time.
If they were "in" the Union, he couldn't free their slaves. For that he declared them "out." For justifying invading them. They were "in."