It's not like the Church tosses out everything Origen wrote. In fact, the only problematic things, IIRC, are those passages where he expresses his weird philosophy. Other works, however, are often read and are very edifying.
Evagrius of Pontus was also anathematized by the Fifth Ecumenical Council, and his works are even more widely read in the Church. They are solid works on prayer and spiritual life.
It was not the Emperor St. Justinian who anathematized, but the Holy Church. If it were only the emperor himself, and he had no authority to do this personally, but even if by force of personality he was able to bend a council to his will, other emperors have done the same thing and their designs have been consigned to the dustbin. The Church cannot be manipulated. Emperors are not all-powerful nor are they immortal.
It is really worth actually getting to know St. Justinian (and the other "controversial" saints, before one slaps a big fat condemnation on oneself by speaking ill of them out of ignorance).