CathInfo.com

I wonder about Traditionalists who believe sincerely that the New Rites are certainly valid, and acted upon such a belief (for example, attending a Diocesan TLM if they're travelling and that's all that is available, when they normally go to a Traditionally valid chapel). There are seemingly priests and lay faithful in the SSPX who have read the arguments against the New Rites, and, while they found them compelling, nonetheless truly believe that the New Rite is certainly valid, and not positively doubtful. I wonder if this would be a mortal sin, because unlike those who are ignorant of the issue, these people know that there are good arguments for invalidity, but truly believe that their arguments for validity are valid, and that they receive a valid Eucharist at these Masses, or valid Absolution in the Confessional. Will acting on the belief that the New Rite is valid have consequences for your soul? Perhaps despite the arguments for objective positive doubt, those who believe it is valid can claim that because the Church hierarchy is not here to decide one way pr another, both positions are allowed?