On Tue, 19 Apr 2016 16:20:40 -0400, "Mr. Luddite"
wrote:

Nobody said slavery is moral. Lincoln was morally against it but
recognized he might have to accept some of it in order to save the Union.


Which is why he exempted the states that had not left the union when
he wrote the Emancipation Proclamation. He was willing to live with
their slavery if they stayed in the union. (very notably, Maryland
that bordered DC on 3 sides) In fact Maryland had not freed their
slaves until a month or two before the 13th amendment was ratified in
1864.
It is clear that if the south had stated in the union, they had enough
votes in the senate to stop the 13th amendment.
(another one of those "ifs")
It is debatable whether the emancipation proclamation would have
withstood the SCOTUS if the southern states were still a political
factor in the US. It is quite easy to argue that it was a "taking" and
that the government would have had to make "just compensation" to the
slave holders.
Bear in mind, until the 13th amendment, slavery was a constitutionally
accepted institution. George and Tom had slaves.