Ponder the following:
Suppose the Skverer Rebbe (whom I know nothing about) rules that X is permitted. Suppose that R. Elyashiv and, for good measure, the entire Agudas Yisrael, believes that X is forbidden. Suppose Mr. A believes that R. Elyashiv is the greatest posek alive today, and that the Skverer Rebbe, though a talmid chacham, just doesn't measure up to him. Would Mr. A think it wrong of Skverer chasidim to engage in X, as per their rebbe's ruling? Generally speaking, I think not.
Now replace Skverer chasidim with disciples of R. Hershel Schachter (of YU), and replace X with the belief that Chazal made mistakes in science, or any number of other issues on which R. Schachter (among others) disagrees with R. Elyashiv. Shouldn't the attitude of Mr. A be the same? Shouldn't Mr. A consider it acceptable for R. Schachter's talmidim to follow his views? -- Unless Mr. A thinks that R. Schachter is not a talmid chacham.