Lawful v. unlawful following of the Constitution and US law.
1960s voting issues were in regard to lawful citizens not being allowed to vote due to Jim Crow voting restrictions. Felons however, have broken a federal law which is a violation of their citizenship and therefore has been deemed no longer necessary to allow the right to vote.
Felons have argued this is a violation of the 14th Amendment and being they are still citizens, they should be allowed to vote after completing their sentence.