Absolutely not. One can judge the external forum to decide if a person is wrong/in error (i.e. materially wrong). For an individual to judge another guilty of sin, one would be judging their internal motives that this isn't allowed, based on charity. The Church is the only judge of this.
Here you go again stating that only the Church can judge one guilty of sin. We argued this point on another thread a while ago and you were not able to provide any evidence from Church teaching or moral theology of your assertion.
The Baltimore Catechism of 1891 teaches us the following:
“Question: What is rash judgement?
“Answer: Rash judgment is believing a person guilty of sin without a sufficient cause.”
Fr. Dominic M. Prummer, O.P., in his Handbook of Moral Theology, No. 301, teaches us the following:
“Rash judgment is the firm assent of the mind (whether manifested externally or not) to the existence of sin in another without sufficient reason.”
Note that both the Baltimore Catechism and Fr. Prummer place a qualifier that makes one guilty of rash judgment, that is, without a sufficient cause or reason. However, what if one does have a sufficient cause or reason? Then he is not guilty of rash judgment.
Fr. Thomas Slater, S.J., in his A Manual of Moral Theology, Page 285, is more direct:
“It is no sin to think that another is wicked or has committed a sin if we know it to be a fact.”
The following is from Fr. Paul Kramer's Volume I of To Deceive the Elect:
“The opinion that only the Church authorities are able to judge in matters of heresy, and that we cannot know if someone is a heretic by the application of human reason without a pronouncement of Church authority, is patently absurd, since it is by the application of human reason to the matters of faith that ecclesiastical judges reach their conclusions in heresy cases and pronounce judgment.”
Pax Vobis, your assertion is of your own invention.