Why did the Radical Republicans oppose Lincoln's plan?

They believed that his reconstruction plan, the 10% Plan, was too lenient on the former Confederate States. His plan concluded that only 10% of a state's population had to pledge allegiance with the U.S. to gain statehood again. They believed that the Freedmen population, who would gain their right to vote, would fill the 10% needed to gain statehood and the original seceders would not be the ones pledging.