If validity is your only litmus test for attendance, then had you lived in England under Henry VIII, you’d certainly have become Anglican, whose rites were certainly valid for many decades.
I didn't think Sean was saying you should go, only that if, being ignorant of the problems in the NO, you did go, while in a state of grace, and well disposed, you would receive grace from the valid sacrament.
I don't see how it makes sense to deny *that* unless you say its valid.
Its a separate question whether a man, knowing the issues, is ever justified in going to the Novus Ordo, or whether *such a man* would be truly well disposed. But Sean suggested it would at the least be doubtful that that would be the case.