New Canon Law Abrogates Old Penalties
Are Pope Gregory III's ban of horse meat and Pope Pius XII's ban of reading communist literature (if he even did—I am still confused regarding this matter) still in effect? I am confused as to whether either can lead to excommunication.
Pope Gregory III's ban was a penal act by the authority of the Apostolic See. Pope Pius XII's decree against reading communist literature was based on the 1917 Code of Canon Law (canon 1399). As such, these penal laws are abrogated per the 1983 Code of Canon Law. That's not to say these actions are now moral to undertake, it simply means that they no longer carry canonical penalty.
The 1983 Code of Canon Law:
Can. 6 §1. When this Code takes force, the following are abrogated:
1. the Code of Canon Law promulgated in 1917; . . .
3. any universal or particular penal laws whatsoever issued by the Apostolic See unless they are contained in this Code.