That person going into the movies is already being oiver one averia. By removing his yarmulke he is now oiver 2 averiros.
IIRC, that is indeed R’ Moshe’s reasoning.
BOR – Listen Chavereim, Torah does not forbid you from watching a screenplay.
Please inform us of who you got s’micha from allowing you to decide matters of Jewish law.
On other threads, I’ve posted a teshuva from Chacham Ovadiah Yosef in which he explains clearly that there are several serious issurim involved in viewing most secular media, and quotes several other gedolim who had the same opinion.