Fr. Daniel Themann of SSPX - Freemasons Commit No Sin by Being a Freemason. According to Fr. Themann of the SSPX most Freemasons are "ignorant" and therefore commit no sin by being a Freemason, is this Catholic Doctrine?
No, ignorance does not excuse a mason from the mortal sin of being a mason. Fr. Thiemann is wrong, like many others who have been taught the same about Protestants, Jews, and other false religions.
Those who perish do not receive the love of truth in order that they might be saved. Therefore, God will send them the operation of error, to believe lying, so that all may be judged who have not believed the truth but have consented to iniquity. (II Thesss. 2:10-11)
The excuse of ignorance is denied those who know the commandments of God, but neither will those who do not know be without punishment. "For, as many as have sinned outside the law shall also perish outside the law" (Romans 2:12). Without faith in Christ, no man can be delivered; therefore, they will be judged in such a way that they perish. "The servant who does not know his Lord's will, and who commits things worthy of stripes, shall be beaten with few stripes; whereas, the servant who knows his Lord's will, shall be beaten with many stripes" (Lk. 12:47 48). Observe here that it is a more serious matter for a man to sin with knowledge than in ignorance. And yet, we must not take refuge on this account to shades of ignorance, to find our excuse therein. Even ignorance which belongs to them who are, as it were, simply ignorant does not excuse anyone so as to exempt him from eternal fire, even were his failure to believe the result of not having heard at all what he should believe. It was not said without reason: "Pour out Thy wrath upon the nations who have not known Thee" (Psalm 78:6), and "He shall come from Heaven in a flame of fire to take vengeance on those who do not know God" (Thess.111:7 8).
(St. Augustine)