I mean ... it's so simple that a child can figure it out, and you don't need 6 years in Trad seminary.
MAJOR: No Salvation Outside the Church. [Dogma -- defined multiple times]
MINOR: Heretics, schismatics, Jews, Muslims, pagans CAN be saved somehow. [held by most Trads]
CONCLUSION: Heretics, schismatics, Jews, Muslims, pagans can be IN the Church somehow.
Conclusion is unavoidable for those who adhere to the Minor, short of denying Catholic dogma.
So, then ... what is this Church that can include not only actual Catholics who are members of the Church and visibly belong to it, and yet can also include and have within various heretics, schismatics, Jews, Muslims, pagans, etc. ... who are visibly separated from the Church? Why it's the Church which SUBSISTS in the Catholic Church (as the visible core) but which is not co-extensive with her visible boundaries. So, then truly, these folks ARE our "separated brethren", brethren (formally) because they are in the same Church with us, whether they know it or not, and are therefore infused with the supernatural life of the Holy Trinity, but separated (materially), visibly, since they have various doctrinal differences and fall short of that fullness of truth that actual Catholics have.
Then, since we please God and save our souls by following even erroneous consciences, then, since we have a right to please God and to save our souls, then we have right to follow our (even erroneous) consciences. In fact, if we attempt to impede people from following said consciences, we imperil their salvation and can cause them to displease God ... which of course borders upon blasphemy. And yet ... here we have most Tradtards buying into it hook, line, and sinker, essentially embracing the same doctrinal errors as Vatican II, but merely holding on to their smells and bells.