So the Pope has lifted the excommunications of the four illicitly consecrated Bishops of the Society of St. Pius X. For those who don't follow Catholic inside baseball, the SSPX considers itself an ultra-traditionalist group with the goal of attempting to preserve the pre-Vatican II patrimony of the Catholic Church in the face of Vatican II reforms. Assuming I have it right, which I might not because I don't have an intense interest in the matter, these four Bishops were consecrated - validly, that is to say, they really did sacramentally become bishops - but illicitly, that is, without the juridical permission of Rome. As a result they were excommunicated by Pope John Paul II. It is that excommunication which has been lifted by Pope Benedict XVI.
That is just background for what interests me in particular here, which is the hubbub over the fact that one of the four Bishops is apparently a Holocaust denier. (Note: I haven't been able to view the video at dotCommonweal as of this writing, but we can stipulate all of this for my purposes here).
Now Bishop Williamson was not excommunicated for being a Holocaust denier: he was excommunicated for his deliberate illicit consecration as a Bishop. The one really has nothing to do with the other. Nevertheless, and understandably, lifting his excommunication has created a bit of a storm. Many people feel that Holocaust denial is so gravely immoral - not to mention loopy - that it warrants excommunication in itself; and I am sympathetic to this view.
However, that directly raises the general question of what moral wrongs are so gravely wicked that they warrant excommunication. Keep in mind that even a serial killer is not excommunicated on account of being a serial killer: he may be damned, if he does not repent, but he is not excommunicated.
Holocaust denial is inexcusably crazy and wicked, but it does not involve advocacy and support of an existing legal right to murder Jews. Furthermore, it is not Catholic doctrine that some historical event such as the American Revolution, the Civil War, the moon landing, or the Holocaust actually occurred. On the other hand, opposition to a legal right to abortion is Catholic doctrine. So if the time has come to start excommunicating the wicked - a proposition about which I reserve judgment - they had better get in line behind the heretics.