I was always under the impression that the particular case of watching a movie was a strong example of belief as attire - forming an opinion (and discussing it at length) about particular bits of a movie everybody watched is a good way to show that you paid attention to details and are capable of complicated analysis (disclaimer: of course there are genuine movie critics, as well as movies that are actually bad and movies that are actually good. I just think the above explains the most common scenario).

I think your general point is correct, though, but I wouldn't say the phenomenon is caused primarily by sneering. People discount opinions they disagree with in general, which includes sincere criticism, and this effect is further strengthened if they get the impression that the differing opinion is offered with insulting as a primary goal.