Why did many Northerners oppose Lincoln's plan for Reconstruction?

(1865€“1877)
is the term used to describe the historical period after the end of the Civil War(1861€“1865).
Because Abraham Lincoln was assassinated in 1865, he did did not actually preside over this
contentious post-war era.

Only by late 1864 did it become obvious that Union
victory in the war against the South was inevitable. Opposition to Lincoln during the
presidential campaign of the first half of 1864 was formidable. Potential challengers to
Lincoln, John Fremont and Salmon Chase, emerged among Republicans. The Civil War had lasted for
years and was far bloodier than anyone could have imagined, and Lincoln's reelection became
likely only after the Union captured Atlanta in September 1864.

Opposition
to Lincoln's nascent plan for Reconstruction came from Congressional leaders. Lincoln's plan for
Reconstruction was promulgated in December 1863. Known as the Ten Percent Plan, states that had
left the Union could be readmitted when at least ten percent of their prewar...