Benedict noted, “there is no doubt that on this point we are faced with a profound evolution of dogma” and that since the 1950s “the understanding that God cannot let go to perdition all the unbaptized … has been fully affirmed.”
Karl Rahner remarked that the biggest theological revolution at Vatican II was in fact the notion that salvation is possible for those outside the Church, and yet the conservative group at the Council didn't give it a second thought.
That's because the destruction of EENS dogma had been well under way for a few hundred years, and even the likes of Archbishop Lefebvre believed in a flavor of Anonymous Christianity.
In any case, I have long argued that this was in fact the chief problem at Vatican II, but most Traditional Catholics refused to touch it.
Major: There's no salvation outside the Church.
Minor: Heretics, schismatics, and infidels can be saved.
Conclusion: Heretics, schismatics, and infidels are in the Church.
Thus you get Vatican II subsistence ecclesiology, where the visible core is the Catholic Church, in which the Church subsists, but the boundaries of the Church extend outside of this core.
Thus it's true that these heretics, schismatics, and even infidels are "separated brethren", materially separated, but formally united to and within the Church.
Even Religious Liberty derives from this subjectivist soteriology.
Major: People have a right to please God and to save their souls.
Minor: People please God and save their souls even by following false beliefs.
Conclusion: People have a right follow their false beliefs.
In fact, as per what you right, if you were to prevent them from pursuing their false beliefs, you may be hindering their salvation.