My understanding of the situation is that SSPX members were automatically excommunicated for consecrating bishops without permission. They broke the rules. No one decided to excommunicate them; they excommunicated themselves by doing something they did not have the authority to do, and the Vatican's statement on the matter pretty much says the same thing. Whether you oppose Vatican II or support the Latin Mass is irrelevant. The problem is that SSPX claims to be Roman Catholic, which entails being subject to the authority of the Pope, but they deliberately acted against the Vatican by consecrating bishops without permission.