Your thread wasn't breaking any rules, you're right. However, it was not discussion-oriented. Yes, you could have added a disclaimer telling people to explain their choice, but in my experience as a moderator such threads do not end well. They are prone to people posting ego-inflationary things, in addition to my previous explanation for why such a thread premise was a poor one to begin with (and as such precludes any discussion, including justification of said movie choices).