Question

radical republicans in Congress opposed President Lincoln's plan for reconstruction because they thought it was too

Answer 1

Too moderate

Radical Republicans wanted stronger punishment to be imposed on the South than Lincoln's plan  called for, and wanted a larger role for the federal government in the overall reconstruction plan.  Lincoln's plan called for a path of forgiveness and rebuilding for the South.  His 10 percent plan said that as soon as 10% of a state's voters would swear an oath of allegiance to the Union, the state could be readmitted to the Union.

Answer 2

They felt he was being too soft on the South. They wanted the South to be punished more. They wanted the Federal government to be more in control.