That was in 1962, as I recall. Archbishop Rummel got away with excommunicating the three segregationists (one of whom, I believe, is still alive and still excommunicated) because he was on the 'right' side of history. An excommunication today, in a different political and ecclesiastical context, might well have unforeseen and even disastrous consequences for the Church.

Jesus came to proclaim the  Kingdom of God, not the Code of Canon Law. As far as we know, he excommunicated no one -- not even Judas who betrayed him or Peter who denied him. Should we learn from him?