Adams is heretical for inculcating the proposition that heretics are able to "grow and progress in union with Christ," while outside the Church. There is no union with Christ if you are CUT OFF from Him.
Sadly, Clare has made a feeble attempt at using verbiage of popes to justify this monstrosity of a belief:
He refers to protestants as Christians which Im sure some on this forum would consider in and of itself heretical...
Protestants who are validly baptized have the indelible character imprinted on their souls, which distinguishes them as FALLEN AWAY CHRISTIANS. When a person speaks of heretics as Christians in such a way as to imply that they are okay in their false religion, however, this smacks of heresy.
Pope Pius IX kind of did that too:
It is therefore by force of the right of Our supreme Apostolic ministry, entrusted to us by the same Christ the Lord, which, having to carry out with [supreme] participation all the duties of the good Shepherd and to follow and embrace with paternal love all the men of the world, we send this Letter of Ours to all the Christians from whom We are separated, with which we exhort them warmly and beseech them with insistence to hasten to return to the one fold of Christ; we desire in fact from the depths of the heart their salvation in Christ Jesus, and we fear having to render an account one day to Him, Our Judge, if, through some possibility, we have not pointed out and prepared the way for them to attain eternal salvation.
He's not saying "Go ahead and worship Christ in your own way and you'll be saved, after all you're Christians!"
And Leo XIII:
His empire includes not only Catholic nations, not only baptized persons who, though of right belonging to the Church, have been led astray by error, or have been cut off from her by schism, but also all those who are outside the Christian faith; so that truly the whole of mankind is subject to the power of Jesus Christ.
(see he distinguishes between baptised non-Catholics, and those outside the Christian faith.)
You did not present the context of his encyclical.
He is simply showing in this encyclical that Jesus Christ is the Supreme Ruler over the whole world. He's not coming even close to heretical, and nor is he implying that there is salvation in any so-called Christian religions or non-Christian religion (while the baptized heretic has the Christian character on his soul, his religion is NOT CHRISTIAN - but Satanic).
Blessed Margaret Mary Alacoque's reception of the Divine command to propagate the worship of the Sacred Heart, many letters from all parts, not merely from private persons but from Bishops also were sent to Pius IX begging that he would consent to consecrate the whole human race to the Most Sacred Heart of Jesus. It was thought best at the time to postpone the matter in order that a well considered decision might be arrived at...
This world-wide and solemn testimony of allegiance and piety is especially appropriate to Jesus Christ, who is the Head and Supreme Lord of the race. His empire extends not only over Catholic nations and those who, having been duly washed in the waters of holy baptism, belong of right to the Church, although erroneous opinions keep them astray, or dissent from her teaching cuts them off from her care; it comprises also all those who are deprived of the Christian faith, so that the whole human race is most truly under the power of Jesus Christ. For He who is the Only-begotten Son of God the Father, having the same substance with Him and being the brightness of His glory and the figure of His substance (Hebrews i., 3) necessarily has everything in common with the Father, and therefore sovereign power over all things. This is why the Son of God thus speaks of Himself through the Prophet: "But I am appointed king by him over Sion, his holy mountain. . . The Lord said to me, Thou art my son, this day have I begotten thee. Ask of me and I will give thee the Gentiles for thy inheritance and the utmost parts of the earth for thy possession" (Psalm, ii.). By these words He declares that He has power from God over the whole Church, which is signified by Mount Sion, and also over the rest of the world to its uttermost ends. On what foundation this sovereign power rests is made sufficiently plain by the words, "Thou art My Son." For by the very fact that He is the Son of the King of all, He is also the heir of all His Father's power: hence the words - "I will give thee the Gentiles for thy inheritance," which are similar to those used by Paul the Apostle, "whom he hath appointed heir of all things" (Hebrews i., 2).
And [anti]Pope Benedict XV:
In every age it has been the concern of the Roman Pontiffs, Our predecessors, and likewise it concerns Us greatly, that Christians who have, unfortunately, withdrawn from the Catholic Religion should at length be recalled to us as a forsaken Mother.
While I have no qualms with this particular statement of antipope Benedict XV, since he is acknowledging them as
fallen away Christians, I reject him on
other grounds.