The errors of Vatican II will be corrected by Vatican III, unless other circumstances make that a moot point. And personally, I think the latter "other circumstances" scenario might be the more likely one. Vatican II was a deliberate strategy to "Protestantize" the Catholic Church. Fifty years later, the institutional Catholic Church as we knew it has made great progress in that regard ... which means it is disappearing just like all the other Protestant congregations.
In several decades, groups like the FSSP and SSPX will be the only Catholic institutions left in many western countries. They won't even need permission from local bishops to open their own apostolates because nobody will care enough about "Catholicism" to oppose them.
I would argue that not speaking out against them makes it easier to ignore them. It also means that others who will join the parish solely because it has the Latin Mass, not because there are issues with Vatican II. By not speaking out from the pulpit, the FSSP parish looks no different than a non-FSSP parish who celebrates the TLM.
YIKES! VERY well said! I agree with you, to boot.