Confirming someone in error is not charitable. There is no salvation outside the Church. This was the consistent teaching of the Fathers. Now for those who may be in the Church, though not visibly, that is for God to decide. If someone is saved in a heretical sect it is in spite of being in error, not because of it.
"He that believeth and is baptized, shall be saved: but he that believeth not shall be condemned."- Our LORD Jesus Christ
“We know that salvation itself is a property of the One Church, and that no one can be outside of the catholic Church and yet share the Faith of Christ, or be saved...Neither do we offer any part of that hope to the ungodly heretics, but we place them entirely outside of that hope; indeed, they have not the least participation in Christ, but vainly assume for themselves that saving Name.”- St John Chrysostom
“The universal [catholic] Church is a great paradise...and should anyone be found in the Church ailing with heretical error from the teaching of the serpent...then he is cast out of this paradise, even as Adam was cast out from the paradise [of old].”- St John Chysostom
“I therefore, yet not I, but the love of Jesus Christ, entreat you that ye use Christian nourishment only, and abstain from herbage of a different kind; I mean heresy. For heretics mix up Jesus Christ with their own poison, speaking things which are unworthy of credit, like those who administer a deadly drug in sweet wine, which he who is ignorant of does greedily take, with a fatal pleasure leading to his own death.” - St Ignatius the Godbearer
“Just as the fishermen hide the hook with bait and covertly hook the fish, similarly, the crafty allies of the heresies cover their evil teachings and corrupt understanding with pietism and hook the more simple, bringing them to spiritual death”- St. Isidore of Pelusium
“Heresy separates every man from the Church.”- 7th Ecumenical Council
Why this modern timidness in proclaiming the Truth that salvation is only found in and because of the Church?